Using your plastic opening tool, pry under the back case starting with the top as marked by red circle.

There is a small clip at the top of the phone that must be released in order to remove the back case.

The volume button and camera button are held in by the back case. Volume button pictured. Camera button opposite.

REASSEMBLY ONLY: Replace volume and camera buttons in place. Then, insert the top of the back case FIRST and squeeze together clips as you work toward the bottom of the phone.