How can i use the object pool script to create and destroy gameobjects ?

The ObjectPool script:

 using UnityEngine;
 using System.Collections.Generic;
 
 public class ObjectPool
 {
     private GameObject prefab;
 
     private List<GameObject> pool;
 
     public ObjectPool(GameObject prefab, int initialSize)
     {
         this.prefab = prefab;
 
         this.pool = new List<GameObject>();
         for (int i = 0; i < initialSize; i++)
         {
             AllocateInstance();
         }
     }
 
     public GameObject GetInstance()
     {
         if (pool.Count == 0)
         {
             AllocateInstance();
         }
 
         int lastIndex = pool.Count - 1;
         GameObject instance = pool[lastIndex];
         pool.RemoveAt(lastIndex);
 
         instance.SetActive(true);
         return instance;
     }
 
     public void ReturnInstance(GameObject instance)
     {
         instance.SetActive(false);
         pool.Add(instance);
     }
 
     protected virtual GameObject AllocateInstance()
     {
         GameObject instance = (GameObject)GameObject.Instantiate(prefab);
         instance.SetActive(false);
         pool.Add(instance);
 
         return instance;
     }
 }

And the script i'm using to create the gameobjects. This script is attached to a empty GameObject. The part that create the gameobjects in the Clone() is working fine with the pooling.

The problem is in the Update()

I want that when i change the value of SpaceShipCount in the Inspector while the game is running in real time to remove/release/destroy all the already existing gameobjects and create new once according to the new value of SpaceShipCount.

And i don't want it to be like a gun bullet effect i want all the gameobjects to release at once and then to create the new once.

The problem is that when i change the SpaceShipCount value it's releasing(destroying) only one object. For example if i'm running the game and i have 100 objects when i change the SpaceShipCount value to 1 i want to have 1 new gameobject but not gun bullet shooting effect but more like destroying effect. To release(destroy) all objects and create new.

 using System;
 using UnityEngine;
 using Random = UnityEngine.Random;
 using System.Collections;
 using System.Collections.Generic;
 using System.Linq;
 
 public class InstantiateObjects : MonoBehaviour
 {
     public GameObject Spaceship;
     public int spaceshipsStartingHeight = 20;
     [HideInInspector]
     public GameObject[] spaceships;
 
     // for tracking properties change
     private Vector3 _extents;
     private int _spaceshipCount;
     private float _spaceshipSize;
     private ObjectPool bulletPool;
     private GameObject o;
 
     /// <summary>
     ///     How far to place spheres randomly.
     /// </summary>
     public Vector3 Extents;
 
     /// <summary>
     ///     How many spheres wanted.
     /// </summary>
     public int SpaceShipCount;
     public float SpaceShipSize;
 
     // Use this for initialization
     void Start()
     {
         Clone();
     }
 
     private void OnValidate()
     {
         // prevent wrong values to be entered
         Extents = new Vector3(Mathf.Max(0.0f, Extents.x), Mathf.Max(0.0f, Extents.y), Mathf.Max(0.0f, Extents.z));
         SpaceShipCount = Mathf.Max(0, SpaceShipCount);
         SpaceShipSize = Mathf.Max(0.0f, SpaceShipSize);
     }
 
     private void Reset()
     {
         Extents = new Vector3(250.0f, 20.0f, 250.0f);
         SpaceShipCount = 100;
         SpaceShipSize = 20.0f;
     }
 
     // Update is called once per frame
     void Update()
     {
         if (_spaceshipCount != SpaceShipCount)
         {
             for (var i = 0; i < _spaceshipCount; i++)
             {
                 ReleaseBullet(o);
             }
             _spaceshipCount = SpaceShipCount;
             Clone();
         }
     }
 
     private void Clone()
     {
         if (Extents == _extents && SpaceShipCount == _spaceshipCount && Mathf.Approximately(SpaceShipSize, _spaceshipSize))
             return;
         
         var withTag = GameObject.FindWithTag("Terrain");
         if (withTag == null)
             throw new InvalidOperationException("Terrain not found");
 
         bulletPool = new ObjectPool(Spaceship, SpaceShipCount);
 
         for (var i = 0; i < SpaceShipCount; i++)
         {
             o = bulletPool.GetInstance();
             o.tag = "SpaceShip";
             o.transform.SetParent(base.gameObject.transform);
             o.transform.localScale = new Vector3(SpaceShipSize, SpaceShipSize, SpaceShipSize);
 
             // get random position
             var x = Random.Range(-Extents.x, Extents.x);
             var y = Extents.y; // sphere altitude relative to terrain below
             var z = Random.Range(-Extents.z, Extents.z);
 
             // now send a ray down terrain to adjust Y according terrain below
             var height = 10000.0f; // should be higher than highest terrain altitude
             var origin = new Vector3(x, height, z);
             var ray = new Ray(origin, Vector3.down);
             RaycastHit hit;
             var maxDistance = 20000.0f;
             var nameToLayer = LayerMask.NameToLayer("Terrain");
             var layerMask = 1 << nameToLayer;
             if (Physics.Raycast(ray, out hit, maxDistance, layerMask))
             {
                 var distance = hit.distance;
                 y = height - distance + y; // adjust
             }
             else
             {
                 Debug.LogWarning("Terrain not hit, using default height !");
             }
 
             //o.transform.Rotate(0.0f,randomNumbers[i],0.0f);
             // place !
             o.transform.position = new Vector3(x, y + spaceshipsStartingHeight, z);
         }
 
         _extents = Extents;
         _spaceshipCount = SpaceShipCount;
         _spaceshipSize = SpaceShipSize;
     }
 
     void ReleaseBullet(GameObject bullet)
     {
         bulletPool.ReturnInstance(bullet);
     }
 }