Remove the two pins on either side of the motor cartridge that hold the arms in place. They should come out with a shake, but you can also use tweezers to grab them if they're not coming out. Keep the pins safe.

Swing the arms out, and remove them by lining up the notch shown in the third image. These arms are two pieces clipped together - they can also be pulled apart.

The arms can easily be replaced with 3d printed parts.