The easiest way to replace your headlight is
http://www.ebay.com/itm/HEADLIGHT-HO...1d467c&vxp=mtr
I have this light on my daily rider and its lasted 2 years so far. The other way is to pull the lens off the current light body and de solder the bulb free. Replace the bulb with a 6 volt headlight bulb....(PM me if you go this route for the bulb) and reseal the lens.
be careful when you do the bulb replacement. Wear gloves to prevent body fluid leaks,,