In order to gain access to the rear case, you must remove the back cover and battery. Be sure to have the necessary tools for removing the screws holding the rear case in place.
Turn phone over in the palm of your hand, with the screen facing down.
While grasping the bottom part of the phone with one hand, use your thumb to push the release button at the end of the phone.
This will release the back plate latch; then lift the back plate up and out toward the other end of the phone.
You should now be able to lift the plate completely off the phone.
Hold the phone steady with one hand.
In the other hand use a philips screwdriver to loosen and remove all 3 screws.
Gently lift off the rear case from the front case.