Both the front and rear arms have covers on the bottom secured by two screws. Remove these screws.

In the case of the front arm there is a small board next to the motor with 3 connectors. One receives LED power from the motor control board, a second connects to a LED within the arm itself, and the third is a U.FL antenna connector. Disconnct all three if you need to transfer the board to a replacement arm.

The front arms are similar except that a somewhat larger board extends into the leg.