Hi Tim,
There used to be an instruction with pictures for belt changing on uncle Bobs website, if not then remove the belt cover, rotate the crank until both cam wheel timing marks align the the head/barrel split line and the rotor mark aligns with the casing mark, release the tension pulley center nut, use your virgin pulley extractor to remove the rotor, remove the old belt and fit the new one making sure it is oil and grease free only use fingers to fit the belt no screwdrivers or anything with sharp edges to get it on to the toothed pulleys, re-tension the the pulley, I always rotate the crank to recheck the timing marks before fitting the rotor back.
Good luck
john