Before you start trying to take these apart, go watch this video mentioned in the introduction. Removing these buttons is tricky and frustrating, so study the video carefully and try and follow iPhoneRepairGirl's instructions as exactly as you can.

While removing the spring clips and retainers, it is helpful to keep a finger on the outside of the button to keep it as far inside the frame as possible.

Flip the spring clip up 90 degrees.