how can I make the character jump more by holding the jump button in this script?

hello, I started recently in the world of unity and they gave me this script, I've been 2 months trying to make the character jump more when I keep pressing the jump button, unfortunately I haven't got any result, here is the code if someone can help me :C

using UnityEngine;

using System.Collections;

public class Controller : MonoBehaviour

{

 public class GroundState
 {
     private GameObject player;
     private float width;
     private float height;
     private float length;

     //GroundState constructor.  Sets offsets for raycasting.
     public GroundState(GameObject playerRef)
     {
         player = playerRef;
         width = player.GetComponent<Collider2D>().bounds.extents.x + 0.1f;
         height = player.GetComponent<Collider2D>().bounds.extents.y + 0.2f;
         length = 0.05f;
     }

     //Returns whether or not player is touching wall.
     public bool isWall()
     {
         bool left = Physics2D.Raycast(new Vector2(player.transform.position.x - width, player.transform.position.y), -Vector2.right, length);
         bool right = Physics2D.Raycast(new Vector2(player.transform.position.x + width, player.transform.position.y), Vector2.right, length);

         if (left || right)
             return true;
         else
             return false;
     }

     //Returns whether or not player is touching ground.
     public bool isGround()
     {
         bool bottom1 = Physics2D.Raycast(new Vector2(player.transform.position.x, player.transform.position.y - height), -Vector2.up, length);
         bool bottom2 = Physics2D.Raycast(new Vector2(player.transform.position.x + (width - 0.2f), player.transform.position.y - height), -Vector2.up, length);
         bool bottom3 = Physics2D.Raycast(new Vector2(player.transform.position.x - (width - 0.2f), player.transform.position.y - height), -Vector2.up, length);
         if (bottom1 || bottom2 || bottom3)
             return true;
         else
             return false;
     }

     //Returns whether or not player is touching wall or ground.
     public bool isTouching()
     {
         if (isGround() || isWall())
             return true;
         else
             return false;
     }

     //Returns direction of wall.
     public int wallDirection()
     {
         bool left = Physics2D.Raycast(new Vector2(player.transform.position.x - width, player.transform.position.y), -Vector2.right, length);
         bool right = Physics2D.Raycast(new Vector2(player.transform.position.x + width, player.transform.position.y), Vector2.right, length);

         if (left)
             return -1;
         else if (right)
             return 1;
         else
             return 0;
     }
 }

 //Feel free to tweak these values in the inspector to perfection.  I prefer them private.
 public float speed = 14f;
 public float accel = 6f;
 public float airAccel = 3f;
 public float jump = 14f;  //I could use the "speed" variable, but this is only coincidental in my case.  Replace line 89 if you think otherwise.

 private GroundState groundState;

 void Start()
 {
     //Create an object to check if player is grounded or touching wall
     groundState = new GroundState(transform.gameObject);
 }

 private Vector2 input;

 void Update()
 {
     //Handle input
     if (Input.GetKey(KeyCode.LeftArrow))
         input.x = -1;
     else if (Input.GetKey(KeyCode.RightArrow))
         input.x = 1;
     else
         input.x = 0;

     if (Input.GetKeyDown(KeyCode.UpArrow))
         input.y = 1;

     //Reverse player if going different direction
     transform.localEulerAngles = new Vector3(transform.localEulerAngles.x, (input.x == 0) ? transform.localEulerAngles.y : (input.x + 1) * 90, transform.localEulerAngles.z);
 }

 void FixedUpdate()
 {
     GetComponent<Rigidbody2D>().AddForce(new Vector2(((input.x * speed) - GetComponent<Rigidbody2D>().velocity.x) * (groundState.isGround() ? accel : airAccel), 0)); //Move player.
     GetComponent<Rigidbody2D>().velocity = new Vector2((input.x == 0 && groundState.isGround()) ? 0 : GetComponent<Rigidbody2D>().velocity.x, (input.y == 1 && groundState.isTouching()) ? jump : GetComponent<Rigidbody2D>().velocity.y); //Stop player if input.x is 0 (and grounded) and jump if input.y is 1

     if (groundState.isWall() && !groundState.isGround() && input.y == 1)
         GetComponent<Rigidbody2D>().velocity = new Vector2(-groundState.wallDirection() * speed * 0.75f, GetComponent<Rigidbody2D>().velocity.y); //Add force negative to wall direction (with speed reduction)

     input.y = 0;
 }

}