You need to pull the very top off the motor. Your cam will be exposed. You then need to remove the chain(DO NOT LET IT FALL INTO THE CASE) There are marks on the sprocket the chain rides and the cam holder. You have to line those up and then put the chain back on. Make sure the piston is TDC when you do this. There are other steps invloved like the chain tensioner and stuff. I highly recommend trying to either find your manual or buy a new one. You can probably find a PDF manual online for pretty cheap.