Too many instances

I am trying to replace a prefab with another. I am using Instantiate and Destroy. I am using Raycast to target the prefab with the mouse.

It works but it instantiates many prefabs instead of just one. And the number of instances that it instantiates varies from 6 instances to 1.

Can someone please help me to find the problem?

C# code:

 using UnityEngine;
 using System.Collections;
 
 public class Srp_LandPositioner : MonoBehaviour {
 
     // Found Mouse select code here:
     // http://answers.unity3d.com/questions/23711/destroy-object-on-mouse-click.html
     
     // Update is called once per frame
     void Update() 
     {
            //this if check for the mouse left click
            if(Input.GetMouseButtonUp(0))
            {
     
               Ray ray = Camera.main.ScreenPointToRay(Input.mousePosition);
                RaycastHit hit;
             
               //this if checks, a detection of hit in an GameObject with the mouse on screen
               if(Physics.Raycast(ray, out hit))
             {
                  Debug.DrawRay (ray.origin, hit.point);
                 print (hit.collider.gameObject.name);
                 
                 GameObject newApple = Instantiate(GameObject.Find("Pre_Apple"), hit.collider.gameObject.transform.position, hit.collider.gameObject.transform.rotation) as GameObject;
                 newApple.name = "Apple " + newGameLand.transform.position.x + ", " + newGameLand.transform.position.z;
                    Destroy(GameObject.Find(hit.collider.gameObject.name));
                 
                }
         }
     }
 }