How to replace prefab at the same location?

Hi everyone,

I am trying to make a tree that grows every ten seconds. I made 4 prefabs (germ, small, medium and big) and I want the object to change every 10 seconds. I manage to make the timer work, but i don't know how to replace PlantStage01 with PlantStage02. I tried with instantiate but it seems like I'm doing something wrong.

 using UnityEngine;
 using System.Collections;
 
 public class PlantGrowth : MonoBehaviour 
 {
 
     public float plantGrowth = 1;
     public float plantSize;
     void Start () {
 
     }
     
     void Update () {
     
         plantSize = plantSize + plantGrowth * Time.deltaTime;
 
         if (plantSize>=10)
             Destroy (gameObject);    
             Instantiate (Resources.Load ("Prefabs/PlantStage02"));
 
     }
 }

All I achieve is that it keep creating PlantStage02 every frame until the gameObject is destroyed, then the script is destroyed with it, and nothing happens anymore. What I want is for the prefab PlantStage01 to disappear and be replaced by PlantStage02.

Can anybody help?

Thank you