Remove the screw from the magazine catch. After the screw is removed, the magazine catch assembly should come apart in four pieces (screw, button, spring, arm).
Punch out the small receiver pin from the right side of the gun (see picture). It is important that you do not try to do this from the right side. One end of the pin is textured to prevent it from coming loose, and pushing this end through the receiver may cause minor damage.
Set the selector to "semi" and remove the fire control assembly from the lower receiver.