Using the plastic opening tool, pry open the body of the phone, starting at the bottom of the phone (this tends to be the easiest place to start).

Double check to make sure the SIM card is removed from its housing. You will not be able to pry open the body of the phone if the SIM card remains in its housing.

Continue by sliding the opening tool around the perimeter of the phone. You should hear multiple clicking sounds as you complete this, indicating the clips are becoming unlatched.

This may take a few tries to get correct. Don't give up if it doesn't work the very first time.