I have a '74 Ciao, if they are the same, loosen and take off the brake cable, slack the chain and remove from the sprocket, remove the nut from the center of the belt pulley, loosen the two big bolts on either side - the wheel should then be loose. I had to remove the bolts on either side to loosen the fender too. Lift up the rear of the bike and the wheel should come out from below. A real pain, I've done it three times in the last month with a slow leak in the tube. Getting the pulley back on the shaft may be difficult. You may have to loosen the engine bolts to slack the belt to get it back on. Good luck.