press e to speek

I have this old NPC chat box system that was given to me. I do not know where to edit this to remove the chat box and just have a button floating above the NPC’s head. I would like the button to load a new level when clicked.

her the npc chat box system script

     using UnityEngine;
     using System.Collections;
     
     //Put this script on your NPC
     
     public class NPCTalkBox : MonoBehaviour
     {
         public string npcTextMessage = "Hello, I'm an NPC"; //Message to show on the screen
         public Rect popupBox = new Rect(0.25f, 0.75f, 0.5f, 0.1f); //This is the size of your popup box in screen size
         public Rect messageBox = new Rect(0.1f, 0.7f, 0.8f, 0.2f); //This is the size of your message box in screen size
         public Transform player; //The player that we're checking the distance from
         public float minDistance = 1f; //How far away we have to be in order to show the message
         
         private bool inRange = false; //Controls showing the 'ready to talk' message
         private bool showText = false; //Controls showing the NPC message
         
         void Start()
         {
             //If you've forgotten to setup the player in the Inspector.. then I'm going to send you an angry message
             if(player == null)
             {
                 Debug.LogError("Variable 'player' not set up on "+gameObject.name+". Disabling the associated script.");
                 this.enabled = false;
             }
         }
         
         void Update()
         {
             if(Vector3.Distance(transform.position, player.position) <= minDistance) //Are we close enough?
             {
                 //Toggle showing the "press X to talk" message
                 inRange = true;
                 
                 //Toggle showing the text every time we press Fire1
                 if(Input.GetButtonDown("Fire1"))
                 {
                     showText = !showText; 
                 }
             }
             else
             {
                 //Hide the text if we walk out of range
                 inRange = false;
                 showText = false;
             }
         }
         
         void OnGUI()
         {
             if(inRange && !showText)
             {
                 GUI.Box(new Rect(Screen.width*popupBox.x, Screen.height*popupBox.y, Screen.width*popupBox.width, Screen.height*popupBox.height), "Press to talk to "+gameObject.name+".");
             }
             
             if(showText)
             {
                 GUI.Box(new Rect(Screen.width*messageBox.x, Screen.height*messageBox.y, Screen.width*messageBox.width, Screen.height*messageBox.height), npcTextMessage);
             }
         }
     }
 

ples help