The second step is to remove the side plates that rest against your palms. This can be done with an iFixit opening tool or some iFixit opening picks.

If you have an opening tool, insert it near the tip as shown and "pry" the side plate away from the controller. You'll hear a click as the clips come loose. Slide the tool around the plate, prying as you encounter resistance, until it comes free.

If you also have an opening pick, it can be helpful to insert one near the bottom once the plate loosens. Otherwise, the clips at the bottom may reconnect while you're working on the others.

This takes a bit of force, but apply it slowly at first. If the prying tool slips, you could end up jabbing yourself.

If you only have opening picks, press them between the side and front plates. At first, you'll only be able to insert them in certain spots; push them in as deeply as you can until you have a few in place. Then, wiggle and slide the picks until you hear the clips loosen.

The clips can be difficult to locate, so you may need to experiment a bit. The picture may help give you an idea how to get started.