dead easy, did mine when i bought the car,
take off the heater control panel cover,
remove the 4 screws and remove the heater control unit
take ashtray out
think theirs a few more screws which u remove and then u can get to a little holder which houses the bulb, i think its a main dealer only bulb, cost me around 2.50 to 3 quid
it lights up the cig lighter and ashtray too
its dead easy to do and self explanitory once u start to remove all the screws