Lift the back cover from the phone and remove it.

If the back cover is still stuck to the midframe, slide an opening pick around the edges of the phone until the cover separates completely.

During reassembly:

This is a good point to test your phone's functionality before sealing it up. Use this guide to run a hardware test. Be sure to power your phone back down completely before you continue working.

Follow this guide to replace the back cover adhesive.