Disconnect the battery connector from the controller board

At the bottom, two stickers hold the audio wires in place, remove them.

Remove the 5 screws holding the battery pack (2 center, 3 surrounding it), place them on an appropriate drawing of the battery pack.

Carefully remove the battery pack, and remember how those speaker wires were put in there at the bottom.

If you want to replace the battery, you're done here. Just work backwards from here and reassemble everything.