Grab the front cover.

Push the L1 and R1 buttons down and away from the cover.

This will remove the buttons in place.

Often when you go to put the case back together, the rubber pads for the L1/R1 buttons get scrunched out the place. Instead of putting those buttons in before putting the case together. leave them off. Once you have the case back together, you can snap them in from the outside.