Use the 5mm allen wrench to remove the screw connecting the A-arm and the chassis.

This screw will not back out all the way by simply turning it counter-clockwise. You will want to turn the screw counter-clockwise until it stops moving, then pull the screw the rest of the way out.

Once this screw is removed, the A-arm will be free from the truck! Put the new A-arm in place of the old one and reverse these steps to re-assemble.