I have not took one of a 307 but done citroens before.
Remove the battery and wait at leasty 10mins to discharge airbag,then there should be a few torx screws behind the wheel holding the airbag unit in place,handle with care.make sure the wheel is in the straight ahead position beofre starting as well then remove the nut from the wheel,They can be a little stiff to budge,but use your hands behind the wheel and tap firmly,make sure you tighten the nut properly when your putting it back to gether
mikec
April 2010