Help changing mouse input to touch input.

This script works fine but I cannot understand how to make it work with touch input. I have read and watched tutorials, but I cannot seem to get it done. Could someone change this script to touch so I can get forward with learning and with my project. Thank you in advance.

 using UnityEngine;
 using System.Collections;
     
     public class PauseMenu : MonoBehaviour 
     {
         private bool PopUp;
         public bool pause_button = false;
         public bool resume_game = false;
         public bool quit_to_menu = false;
         public bool    standard = false;
         public bool    scroll = false;
         public bool time_trial = false;
         public bool quitgame = false;
         public bool upgrades = false;
         
         void OnMouseDown()
             {
             if(standard)
                 {
                 StartGame.Lvl = 1;
                 GameObject Sphere = GameObject.Find("Sphere");
                 Sphere.rigidbody.isKinematic = false;
                 Sphere.rigidbody.AddForce(0f, 600f, 0f);
                 }
             
             if(scroll)
                 {
                 StartGame.Lvl = 2;
                 GameObject.Find("Sphere").rigidbody.isKinematic = false;
                 GameObject.Find("Sphere").rigidbody.AddForce(0f, 600, 0f);
                 }
             
             if(time_trial)
                 {
                 StartGame.Lvl = 3;
                 GameObject Sphere = GameObject.Find("Sphere");
                 Sphere.rigidbody.isKinematic = false;
                 Sphere.rigidbody.AddForce(0f, 600, 0f);
                 }
             
             if(upgrades)
                 {
                 
                 GameObject Cam =  GameObject.Find("!Camera");
                 Cam.animation.Play("CameraLaptop");
                  GameObject.Find("Laptop/Static").renderer.enabled = false;
                 StartCoroutine(Up_Delay());
                 }        
             
             if(quitgame)
                 PopUp = true;
             
             if(pause_button)
                 {
                 Time.timeScale = 0.00001f;
                 GameObject Pausemenu = GameObject.Find("PauseMenu");
                 foreach(Transform child in Pausemenu.transform)
                         child.gameObject.SetActive(true);
                 GameObject PU =  GameObject.Find("PowerUps");
                 foreach(Transform child in PU.transform)
                         child.gameObject.SetActive(false);
                 
                 }
             
             if(resume_game)
                 {
                 
                 GameObject.Find("Sphere").AddComponent<Resume>();
                 GameObject Pausemenu = GameObject.Find("PauseMenu");
                     foreach(Transform child in Pausemenu.transform)
                         child.gameObject.SetActive(false);
                 GameObject PU =  GameObject.Find("PowerUps");
                 foreach(Transform child in PU.transform)
                     child.gameObject.SetActive(true);
                 }
             
             if(quit_to_menu)
                 {
                 Time.timeScale = 1;
                 Application.LoadLevel(0);
                 }
             }
             
         void DrawInfo()
         {
               Rect rect = new Rect (300, 225, 350, 150); 
             Rect Yes = new Rect(350, 325, 80, 40);
             Rect No = new Rect(525, 325, 80,40);
             if (PopUp)
                    {
                 GUI.Box(rect, "Do you really want to exit?");
                 if(GUI.Button(Yes, "Yes"))
                     {    
                     PopUp = false;
             
                     StartCoroutine(delay(2.0F));
                     }
                 
                 if(GUI.Button(No, "No"))
                       PopUp = false;
                 
                 }
         }    
         
         void OnGUI()
                 {
             DrawInfo();
             }
         
         IEnumerator delay(float waitTime)
             {
             yield return new WaitForSeconds(waitTime);
             Application.Quit();
             }
         
         IEnumerator Up_Delay()
             {
              yield return new WaitForSeconds(1.11f);
             GameObject.Find("Laptop/Upgrades").renderer.enabled = true;
             GameObject.Find("Laptop/BorderDown").renderer.enabled = true;
             }
             
     }