your best bet is to take the whole headlight assembly out, i cant see any other way to do it.
your headlight alignment will probably be out afterwards, so take it to an mot garage, its a 1 minute job to realign them, or use your garage wall and use chalk to mark where your headlights come upto, but park at least 4 metres away from the wall. the adjustments are done by turning the white hex screw on top of the unit.
when i removed my headlights i had to take the bumper off.it has about 15 screws/bolts that secure it.
it'll probably take 2 hours!