place your palm on the helix of the secondary clutch (the part that sticks out further than the rest) and push in with a twisting motion clockwise. this will split the sheaves allowing you to pull the belt off the secoudary and then off the primary.
setting the parking brake helps too, just remember to flip it back off when done. Also, take a 12mm wrench and use it to turn the secondary, makes it easy on the hands, but it does not seem to wok on my roller set-up.