To remove the coin cell battery, remove the 8 screws securing the base cover. Pry the cover off the system. Identify and unplug the battery cable. Find the coin cell battery and disconnect the cables. Lift the battery out of the system.
To reinstall the coin cell battery, place the battery back in the system and reconnect the cables. Plug in the battery cable. Put the base cover on the system and tighten the eight screws.