Press your thumbnail into the slot between the rear panel and the front casing located on the bottom of the phone. Use a penny or dime if you have trouble using your thumbnail.

With a moderate amount of force, pry the rear panel up and away from the phone. You may need to slide your thumbnail up the crack to separate the rear panel from the front casing.

This can take a little bit of effort. Don't be discouraged if you can't get it right away.