I just swapped mine for one of those purty ones this afternoon. I removed the two screws and just lifted the old cap off. There's a plastic cover/gasket under the metal cap. Just press the new cover on and re install the screws.
It's just a simple swap (unless you empty the resevoir). DON'T squeeze the brake handle with the cap off, or else you'll make a mess. Oh, brake fluid ruins paint, so be careful taking the resevoir cap off (cover your tank and fender with a sheet of plastic.