dont mind the elephant he's gruppy around his bedtime
pop the boot open look at the top of the bood (inside) there are 2 black caps remove these, you can now access the the 2 nuts undo these, you may need to push the unit out with a bar on the back of the stud the nut come off
some time thay stick som times there loose
to get the bulb out just twist the fitting and pull
You may well find that the lamp has sealer around it and will need to be prized out bit by bit with a plain screwdriver. Ensure that you use a thin piece of wood or similar in order to prevent scratches to the paint work. If I were you I would also re seal it when you put it back in to keep rain water out.