type ...Material[] vs Material (materials change at run time)

I am trying to look through an array of materials on a specific game object and change the material at run time. I have read over multiple pages of the scripting reference on materials, game objects, render, transforms, Material.SetTexture and so on. I have also searched and read others answers on similar questions in the forums. All this research points to the fact that I should be using material to form an array which will allow me to set the material element I need to change.

However using the code below I get this:
error CS0029: Cannot implicitly convert type UnityEngine.Material' to UnityEngine.Material

I can not find a resolution for this error and I’m not sure how to convert the material to an array.

What am I doing wrong with my code?

using UnityEngine;
using System.Collections;

public class ChangeMaterial : MonoBehaviour {
	
	//Put the game object with the texture you are changing here.
	GameObject Model;
	public string target;
    // put the first material here.
    public Material material1;
    // put the second material here.
    public Material material2;
	
    bool FirstMaterial = true;
    bool SecondndMaterial = false;    
	Material[] themes;

	
    void Start ()
    {
		
	Model = GameObject.Find (target);
	themes = Model.renderer.materials[4];
	themes[4] = material1;
	Model.renderer.materials[4] = themes; 

    }
     
	void OnMouseDown()
	{
   	 if (!SecondndMaterial)
   	 	{
   		themes[4] = material2;
   		SecondndMaterial = true;
    	FirstMaterial = false;
    	}
     
   	 else if (SecondndMaterial)
    	{
    	themes[4] = material1;
    	FirstMaterial = true;
    	SecondndMaterial = false;
    	}
	}
}

Model = GameObject.Find(target);
themes = Model.renderer.materials[4];
themes[4] = material1;
Model.renderer.materials[4] = themes;

themes is array and materials[4] returning single material. so you can not transfer
single material to material array.

delete all those lines and use like this. Model.renderer.materials[4] = yournewmaterial