disconnect the battery
wait a while, go have a brew or soemthing
come back to themotor
there will be 2 screws/bolts behind the airbag cover and they will either be 5.5mm bolts or T25/30 torxs versions
you may have to spin the wheel to get to them but once they are out you can just yank the edge of the cover and the airbag should come off in one big lump, i think i've got one at home but i can't be too sure where it is
anyhow
once it's off you will find a little yellow plug on the back of it, almost like a phonoe jack, unplug this and thats it, job done
you can now undo the nut in the midle, but only a lillte, make sure there is still a few threads on the nut before you start twatting it from behind with the palms of your hands
it comes off, new one goes on, job done

just make sure that when you pull the original wheel off, the wheels are point in the straight ahead position and that any of the indicator canceling gubbins don't get lost in the wheel removal