So i need to be able to increase the walk speed on button press (Fire1) what do i need to change to do this i am assuming i need a if statement:

Heres the code:

 using System;
 using UnityEngine;
 using UnityStandardAssets.CrossPlatformInput;
 using UnityStandardAssets.Utility;
 using Random = UnityEngine.Random;
 
 namespace UnityStandardAssets.Characters.FirstPerson
 {
     [RequireComponent(typeof (CharacterController))]
     [RequireComponent(typeof (AudioSource))]
     public class FirstPersonController : MonoBehaviour
     {
         [SerializeField] private bool m_IsWalking;
         [SerializeField] private float m_WalkSpeed;
         [SerializeField] private float m_RunSpeed;
         [SerializeField] [Range(0f, 1f)] private float m_RunstepLenghten;
         [SerializeField] private float m_JumpSpeed;
         [SerializeField] private float m_StickToGroundForce;
         [SerializeField] private float m_GravityMultiplier;
         [SerializeField] private MouseLook m_MouseLook;
         [SerializeField] private bool m_UseFovKick;
         [SerializeField] private FOVKick m_FovKick = new FOVKick();
         [SerializeField] private bool m_UseHeadBob;
         [SerializeField] private CurveControlledBob m_HeadBob = new CurveControlledBob();
         [SerializeField] private LerpControlledBob m_JumpBob = new LerpControlledBob();
         [SerializeField] private float m_StepInterval;
         [SerializeField] private AudioClip[] m_FootstepSounds;    // an array of footstep sounds that will be randomly selected from.
         [SerializeField] private AudioClip m_JumpSound;           // the sound played when character leaves the ground.
         [SerializeField] private AudioClip m_LandSound;           // the sound played when character touches back on ground.
 
         private Camera m_Camera;
         private bool m_Jump;
         private float m_YRotation;
         private Vector2 m_Input;
         private Vector3 m_MoveDir = Vector3.zero;
         private CharacterController m_CharacterController;
         private CollisionFlags m_CollisionFlags;
         private bool m_PreviouslyGrounded;
         private Vector3 m_OriginalCameraPosition;
         private float m_StepCycle;
         private float m_NextStep;
         private bool m_Jumping;
         private AudioSource m_AudioSource;
 
         // Use this for initialization
         private void Start()
         {
             m_CharacterController = GetComponent<CharacterController>();
             m_Camera = Camera.main;
             m_OriginalCameraPosition = m_Camera.transform.localPosition;
             m_FovKick.Setup(m_Camera);
             m_HeadBob.Setup(m_Camera, m_StepInterval);
             m_StepCycle = 0f;
             m_NextStep = m_StepCycle/2f;
             m_Jumping = false;
             m_AudioSource = GetComponent<AudioSource>();
             m_MouseLook.Init(transform , m_Camera.transform);
         }
 
 
         // Update is called once per frame
         private void Update()
         {
 
 
 
             RotateView();
             // the jump state needs to read here to make sure it is not missed
             if (!m_Jump)
             {
                 m_Jump = CrossPlatformInputManager.GetButtonDown("Jump");
             }
 
             if (!m_PreviouslyGrounded && m_CharacterController.isGrounded)
             {
                 StartCoroutine(m_JumpBob.DoBobCycle());
                 PlayLandingSound();
                 m_MoveDir.y = 4f;
                 m_Jumping = false;
             }
             if (!m_CharacterController.isGrounded && !m_Jumping && m_PreviouslyGrounded)
             {
                 m_MoveDir.y = 4f;
             }
 
             m_PreviouslyGrounded = m_CharacterController.isGrounded;
         }
 
 
         private void PlayLandingSound()
         {
             m_AudioSource.clip = m_LandSound;
             m_AudioSource.Play();
             m_NextStep = m_StepCycle + .5f;
         }
 
 
         private void FixedUpdate()
         {
             float speed;
 
             GetInput(out speed);
             // always move along the camera forward as it is the direction that it being aimed at
             Vector3 desiredMove = transform.forward*m_Input.y + transform.right*m_Input.x;
 
             // get a normal for the surface that is being touched to move along it
             RaycastHit hitInfo;
             Physics.SphereCast(transform.position, m_CharacterController.radius, Vector3.down, out hitInfo,
                                m_CharacterController.height/2f);
             desiredMove = Vector3.ProjectOnPlane(desiredMove, hitInfo.normal).normalized;
 
             m_MoveDir.x = desiredMove.x*speed;
             m_MoveDir.z = desiredMove.z*speed;
 
 
             if (m_CharacterController.isGrounded)
             {
                 m_MoveDir.y = -m_StickToGroundForce;
 
                 if (m_Jump)
                 {
                     m_MoveDir.y = m_JumpSpeed;
                     PlayJumpSound();
                     m_Jump = false;
                     m_Jumping = true;
                 }
             }
             else
             {
                 m_MoveDir += Physics.gravity*m_GravityMultiplier*Time.fixedDeltaTime;
             }
             m_CollisionFlags = m_CharacterController.Move(m_MoveDir*Time.fixedDeltaTime);
 
             ProgressStepCycle(speed);
             UpdateCameraPosition(speed);
         }
 
 
         private void PlayJumpSound()
         {
             m_AudioSource.clip = m_JumpSound;
             m_AudioSource.Play();
         }
 
 
         private void ProgressStepCycle(float speed)
         {
 
 
             if (m_CharacterController.velocity.sqrMagnitude > 0 && (m_Input.x != 0 || m_Input.y != 0))
             {
                 m_StepCycle += (m_CharacterController.velocity.magnitude + (speed*(m_IsWalking ? 1f : m_RunstepLenghten)))*
                              Time.fixedDeltaTime;
             }
 
             if (!(m_StepCycle > m_NextStep))
             {
                 return;
             }
 
             m_NextStep = m_StepCycle + m_StepInterval;
 
             PlayFootStepAudio();
         }
 
 
         private void PlayFootStepAudio()
         {
         
             if (!m_CharacterController.isGrounded)
             {
                 return;
             }
             // pick & play a random footstep sound from the array,
             // excluding sound at index 0
             int n = Random.Range(1, m_FootstepSounds.Length);
             m_AudioSource.clip = m_FootstepSounds[n];
             m_AudioSource.PlayOneShot(m_AudioSource.clip);
             // move picked sound to index 0 so it's not picked next time
             m_FootstepSounds[n] = m_FootstepSounds[0];
             m_FootstepSounds[0] = m_AudioSource.clip;
         }
 
 
         private void UpdateCameraPosition(float speed)
         {
             Vector3 newCameraPosition;
             if (!m_UseHeadBob)
             {
                 return;
             }
             if (m_CharacterController.velocity.magnitude > 0 && m_CharacterController.isGrounded)
             {
                 m_Camera.transform.localPosition =
                     m_HeadBob.DoHeadBob(m_CharacterController.velocity.magnitude +
                                       (speed*(m_IsWalking ? 1f : m_RunstepLenghten)));
                 newCameraPosition = m_Camera.transform.localPosition;
                 newCameraPosition.y = m_Camera.transform.localPosition.y - m_JumpBob.Offset();
             }
             else
             {
                 newCameraPosition = m_Camera.transform.localPosition;
                 newCameraPosition.y = m_OriginalCameraPosition.y - m_JumpBob.Offset();
             }
             m_Camera.transform.localPosition = newCameraPosition;
         }
 
 
         private void GetInput(out float speed)
         {
             // Read input
             float horizontal = CrossPlatformInputManager.GetAxis("Horizontal");
             float vertical = CrossPlatformInputManager.GetAxis("Vertical");
 
             bool waswalking = m_IsWalking;
 
 #if !MOBILE_INPUT
             // On standalone builds, walk/run speed is modified by a key press.
             // keep track of whether or not the character is walking or running
             m_IsWalking = !Input.GetKey(KeyCode.LeftShift);
 #endif
             // set the desired speed to be walking or running
             speed = m_IsWalking ? m_WalkSpeed : m_RunSpeed;
             m_Input = new Vector2(horizontal, vertical);
 
             // normalize input if it exceeds 1 in combined length:
             if (m_Input.sqrMagnitude > 1)
             {
                 m_Input.Normalize();
             }
 
             // handle speed change to give an fov kick
             // only if the player is going to a run, is running and the fovkick is to be used
             if (m_IsWalking != waswalking && m_UseFovKick && m_CharacterController.velocity.sqrMagnitude > 0)
             {
                 StopAllCoroutines();
                 StartCoroutine(!m_IsWalking ? m_FovKick.FOVKickUp() : m_FovKick.FOVKickDown());
             }
         }
 
 
         private void RotateView()
         {
             m_MouseLook.LookRotation (transform, m_Camera.transform);
         }
 
 
         private void OnControllerColliderHit(ControllerColliderHit hit)
         {
             Rigidbody body = hit.collider.attachedRigidbody;
             //dont move the rigidbody if the character is on top of it
             if (m_CollisionFlags == CollisionFlags.Below)
             {
                 return;
             }
 
             if (body == null || body.isKinematic)
             {
                 return;
             }
             body.AddForceAtPosition(m_CharacterController.velocity*0.1f, hit.point, ForceMode.Impulse);
         }
     }
 }

Any help would be gratefully appreciated.