This is a pretty obvious step but whatever. A more obvoius step would be to remove the side of your case before you begin cuting but again this it up to you. Unless your incredibly brave you might want to preclude this step with some thought and some measuring and marking and whatnot but after the step requring carefull thought you can go to the step requiring powertools . I used an adustible hole cuter set a little over 4 inches if you dont have one you could use a jigsaw or just a normal hole cutter fom your local home depot the adjustible one you can find at woodworkers warehouse. At any rate clamp the piece down very well, wear eye protection, be sure to lubricare with wd40, and most importantly take your time.