It's under the centre console, unscew gear knob, pull the hand brake up, take out the two cup holder rubber bases in front of gear lever and rear ashtray, remove 3 x screws, pull up the centre console over hand brake and remove.
Officially, should advise you disconnect the battery for 15 mins to discharge capacitors in the airbag module before disconnecting/reconnecting the module, whatever you do make sure ignition is NOT on!! Heard about someone setting a BMW E46 cabriolet airbags/sidecurtains everything off once when changing a module!
Make sure you bolt it down and add any earth connections (if fitted) before you turn ignition on.
Yes, match up part number from the label on the module. On this pic
Can see part number starts YS4T,