Adjusting Mouse Sensitivity through GUI.HorizontalSlider (c#)

I have here a character controller script where bothe the movement and camera rotation are in one script. Can anyone help me fix this please? Do i have to access the "publicfloat mousesensitivity = 5.0f;"? if so can anyone help me Thanks again! Also if possible can you guys provide the editted code as a whole kinda sorta still a noob sorry...

Controller script:

 using UnityEngine;
 using System.Collections;
 
 public class Controller : MonoBehaviour {
 
     public float movementspeed = 5.0f;
     public float mousesensitivity = 5.0f;
     public float jumpspeed = 20.0f;
 
     float  verticalRotation = 0;
     public float updownrange = 60.0f;
 
     float VerticalVelocity = 0;
 
     // Use this for initialization
     void Start () {
         Screen.lockCursor = false;
     }
     
     // Update is called once per frame
         
         void Update () {
             CharacterController cc = GetComponent <CharacterController> (); 
 
     //Rotation
         float rotleftright = Input.GetAxis("Mouse X") * mousesensitivity;
             transform.Rotate (0, rotleftright, 0);
 
         verticalRotation -= Input.GetAxisRaw("Mouse Y") * mousesensitivity;
             verticalRotation = Mathf.Clamp (verticalRotation,-updownrange ,updownrange);
                 Camera.main.transform.localRotation = Quaternion.Euler (verticalRotation, 0, 0);
 
 
     //Movement
 
 
         float forwardspeed = Input.GetAxis("Vertical") * movementspeed ;
         float sidespeed = Input.GetAxis("Horizontal") * movementspeed ;
 
         VerticalVelocity += Physics.gravity.y * Time.deltaTime;
 
 
         Vector3 speed = new Vector3 (sidespeed, VerticalVelocity , forwardspeed );
 
         speed = transform.rotation * speed;
 
     
 
         cc.Move ( speed * Time.deltaTime );
     }
 }

Slider Script:

 using UnityEngine;
    using System.Collections;
 
     public class HSlider : MonoBehaviour {
     float hSliderValue = 5.0f;
     // Use this for initialization
     void Start () {
  
     }
  
     // Update is called once per frame
     void Update () {
  
     }
     OnGUI {
         Rect slider = new Rect (50, 30, 100, 30);
         hSliderValue = GUI.HorizontalSlider(slider,hSliderValue,1.0f,100.0f);
     }
  
 }