To remove the side button assembly:

First, unhook the cables from the cable guide so it won't get caught while popping the assembly out

The assembly is held in by some clip-in action from the screw posts on the top shell and screw holes on the assembly. The next step will explain in detail how to pop it out.

Definitely don't pull on the cable to remove like shown in the first picture. The wires are kind of frail.