Remove the battery.

To install a new battery:

Clean your frame with isopropyl alcohol and a lint-free or microfiber cloth.

Before applying adhesive, temporarily reconnect your new battery and place it in its recess to check if it fits and that the cable reaches the socket on the logic board. Disconnect the battery before continuing.

Check out this guide to apply new stretch release adhesive strips to your battery, if it doesn't already come with adhesive installed.

If you don't have stretch release adhesive, use thin, double-sided tape to secure it.