you probably do not need to replace the rings, the burnt valve is the most likely culprit of the low compression in that cylinder. even without replacing piston rings, this is still not a job for the faint of heart or a novice, best guidance i can give, if you are mechanically adept is to buy a haynes repair manual for this specific vehicle (around 20 bucks). I would not even attempt this without at least this bare minimun of info on the vehicle.