Andy - I came across a really detailed instruction on this site somewhere (it even had photos & a step by step process) - see if you can dig it out. If you can't though, it's fairly straightforward. Remove all of the fixings on the door panel (there are a few hidden ones - in behind the inside door pull handle and also behind the plastic "Airbag" sign). Once you have the door panel removed and can see the door airbag box (and before you touch it at all), you have to turn-off the vehicle completely, disconnect the battery in the boot, leave the car for 30 mins (this is sufficient time for any stored charge in the airbag to discharge to protect it from inadvertently deploying). Then, and only then, should you approach the airbag. First of all, disconnect the cable - you have to slide back the little clip on it before it will unplug. Then you can carefully unscrew the fixings and remove the airbag (please store it somewhere safe, away from anyone and ensuring nothing is stored on top of it in the very unlikely event it would deploy - always hold it away from you when moving it). DO NOT reconnect the battery at any time whilst the airbag is disconnected as if you do, it will register an Airbag error code with the vehicle ECU and you will need to travel to a dealer to get it reset (with the associated costs).