Lift up one edge of the battery with an opening pick and lift the battery out of the phone.

To install a new battery:

Remove any battery adhesive remaining on the phone.

Install replacement stretch-release adhesive or double-sided tape such as Tesa tape in the phone's battery cavity where the original adhesive was applied.

Gently set the battery in place. Temporarily connect the battery's connector to the motherboard to ensure that the battery is properly positioned.

Press the battery firmly in place with your fingers.

Disconnect the battery from the motherboard and resume re-assembly.