This is easiest done with the door lifted out. On ours, there are two catches on the hinges. You flip these over (from the oven side to the door) and then lift the door up until it stops at about 70 degrees. The door then lifts out, it's pretty heavy and contains glass. Doors cost half as much as the oven, so it is worth putting a towel on the floor to help cushion it.
the bulb is behind a glass cover in the top right of the oven. Unscrew this anti clockwise- I had to use a pipe wrench toget a grip as it was stuck but it is like a small thick glass jar, about 30mm across, so it's fairly strong. Even so, be careful not to crush it.
Unscrew the bulb, also anti clockwise.
Clean the thread on the cover, if required, and refit.
Bulbs are available from any good DIY shop. It's 15 watt, 250V screwfit.
Phil, January 2009