It generally requires:
- removing the side panel (held on by one or two screws),
- unclipping the front of the case (which should be done carefully, but if you don't force it and unclip the latches one at a time, it isn't difficult),
- removing the screws holding the drive in (generally, there are two screws on each side, but sometimes it's just two screws on one side and a latch on the other),
- unplugging two cables from the back of the drive (one is the data cable, the other is power. The smaller one might have a metal clip holding it in. I normally rock the cables slightly as I pull on them to make it slightly easier to get them off.), and
- sliding the drive out of the front of the case.
You basically reverse those steps to put the new drive in.