On the right side of the snout of the */C, you will see a black plug. Take that off. Use a syringe or something to suck the old oil out, and fill it up with the new stuff. You only need to fill it right up to the threads where the plug goes. You might need a flashlight or something to help you see how much is in there.
Usually it takes 1 and a half bottles of the oil to fill it to the proper level.
Be warned, that stuff smells something fierce.