SpriteChanger.cs

using UnityEngine;
using UnityEngine.UI;
using System.Collections.Generic;

public class SpriteChanger : MonoBehaviour
{
    public List<Sprite> Sprites = new List<Sprite>();
    public float ChangeRate = 2f;

    private Image image;
    private int spriteIndex;

    private void Awake ()
    {
        image = GetComponent<Image>();
    }

    private void Start ()
    {
        InvokeRepeating("ChangeSprite", 0, ChangeRate);
    }

    private void ChangeSprite()
    {
        if (Sprites.Count == 0) return;

        spriteIndex++;
        if (spriteIndex >= Sprites.Count)
            spriteIndex = 0;

        image.sprite = Sprites[spriteIndex];
    }
}