Hi Colin, i had the same problem and its not that hard to do.
You need to start by using a small flat head screw driver to gently lift out the black plastic surround from the clock which should leave the clock unit and a gap surround it, you then will need to use a star bit for the 2 retaining screws that hold the clocks in place and then pull out the clocks.
Now you can disconnect the cables from the back and you have the unit removed.
Now the bulbs are held in by a holder that twists and pulls out, they are in a little drop back so some spic nosed pliers might be helpful and then put the new one in.
You will need to find out what bulbs you need and i think the bulb comes in the plastic holder not sure.
The refit is a revers of the removal i hope this has helped.
Regards mark
Mark, July 2008