This is a 2 man job. Have one person hold him on his back using a warm towel while you trim the very tip of each nail. Cut at a flat angle so the claw is dull not sharper. DO NOT trim any further than about a millimeter from the tip of the claw. If you cut more, you could seriously hurt the guinea pig and cause bleeding.
OK this is important!!!! You must get some ropes and tie the guinea pig down by the arms and lightly by the head. Then, get one of those syringes that you use go give babies medicine, then you get a very high alcohol content spirit, like VODKA, then you give the guinea pig about a shot of vodka. The guinea pig will then be almost on conscious but it will still be able to know what is going on, but it will not feel any pain. So then you get your hack saw blade, and start to SLOWLY, saw of its paws (be sure to go clean through the bone or else the guinea pig might feel some discomfort. Once all four paws are removed make sure to add them to an omelet as they add great flavour. To stop the guinea pigs bleeding take a plastic bottle and melt it over all 4 cuts to seal the wounds. You will then never have to cut his paws again.