You must Disconnect the Battery, Take off Battery Cover, Remove Battery Holder and then yank the battery.
The Black Plastic unlocking ring is TOUGH to get at and remove. I ended up using a long narrow adjustable pipe wrench (NOT a crescent wrench) and sliding down the narrow crack to unlock the ring. Remove from headlamp, take out old bulb, replace with new bulb and reverse steps. DO NOT TOUCH HALOGEN BULB the oil from your skin will burn out the headlight. Good Luck.
Andrew David, May 2007