Boost effect on KeyPress.

I'm building a Spaceship, and I want to add a boost effect on KeyButtonPress. Such as speed up X,amount till you let off the key. I'm verily new to Unity Scripting so any help anyone can give would be awesome. Here is my spaceship script.

using System.Collections; using System.Collections.Generic; using UnityEngine;

public class ShipPlayerController : MonoBehaviour {

 public Projectile Bullet;

 public Camera CameraObject;

 public float FireRate = 0.5f;

 public float MoveSpeed = 18.0f;

 private float FireTimer = 0.0f;

 private Vector3 movement = Vector3.zero;
 private object Horizontal;



 // Use this for initialization
 void Start()
 {

 }

 // Update is called once per frame
 void Update()
 {

     UpdatePosition();
     UpdateFiring();

 }

 void UpdatePosition()
 {

     movement.x = Input.GetAxis("Horizontal") * Time.deltaTime * MoveSpeed;
     movement.y = Input.GetAxis("Vertical") * Time.deltaTime * MoveSpeed;

     gameObject.transform.Translate(movement);

     Vector3 screenPosition = CameraObject.WorldToScreenPoint(
         gameObject.transform.position);


     if (screenPosition.y > Screen.height)
     {

         screenPosition.y = Screen.height;

         gameObject.transform.position =
             CameraObject.ScreenToWorldPoint(screenPosition);
     }

     else if (screenPosition.y< 0)
     {

         screenPosition.y = 0;


         gameObject.transform.position =
             CameraObject.ScreenToWorldPoint(screenPosition);
     }
 }

 void UpdateFiring()
 {

     FireTimer += Time.deltaTime;

     if (Input.GetButton("Fire1"))
     {

         if (FireTimer > FireRate)
         {

             FireTimer = 0;

             DoWeaponFire(); 
       
         }
     }
 }

 void DoWeaponFire()
 {

     Instantiate(Bullet, transform.position, transform.rotation);
 }
   
 }