The quarter panel and rear wing come off as one panel and it's a real ball-ache of a job.
Assuming you've stripped out the interior already...
There's 10 bolts to remove inside plus 1 underneath on the inside of the wheel arch and one more holding the mudflap bracket to the lower wing. You might be better off grinding off this particular bolt or drilling it out rather than risk tearing the ally panel.
There are also 2 self tappers on the upper flange of the panel - you'll see them when you remove two of the bolts inside, though.
Open the tailgate, there are 6 self tappers holding the quarter panel to the E post - remove them.
Remove the piece of trim adjacent to the glass at the rear of the side door. You do this from inside. There's three tophat nuts holding the trim on. Be careful as it's quite fragile.
This will expose four rivits running up the B post. Drill them out.
There is one more rivet to drill out. Open the tailgate and note the speaker mounting bracket. Drill out single the rivet that holds the bracket to the E post. You may leave the other rivets attached if you wish.
Now all that should be holding the wing on is almost a whole tube of sealant. Yes... Really!
Start from the front of the panel and work your way back towards the tailgate. Cut through the sealant with a SHARP Stanley knife to get you started.
Next, thread some steel wire through whatever gap you can CAREFULLY make. Wrap each end of the wire around a wooden clothes peg and with a friend use a sawing motion to cut through the sealant.
DO NOT pull the panel too hard. You WILL break it or bend it if you're too "enthusiastic" as it's only thin ally.
With the panel off the car you can now drill out the spotwelds that hold the 1/4 panel to the rear wing. If you don't have a decent spotwelder, consider the fasteners you use to connect the new rear quarter to the rear wing. Steel and ally will react and cause the ally to corrode. Consider using aluminium pop-rivets to join the two panels together or stainless steel fixings.
*edit* there may well actually be more than 12 bolts holding this wing on. I've just done this job on a 5 door!