How to detect a enemy and change my png according to the enemy position

I am creating a game with the help of PNG sequence of 8.Its is a tower defence game.Now i want that my enemy comes in the range of the tower and when it hits the rang my tower start changing its position accoriding to the enemy position>As these are images in pngs i have to tell the seq that the enemy is at this position now change your png to this tile.

Add a sphere collider (set “Trigger” checked, you need an event not a collision) that will work as your “defense range”, create a script with an OnTriggerStay function where you set your target (if not already set) and call LookAt.