you need to take out the back seat...
if you dont know how:
you need to go one side at a time (or get a friend to do the other side at the same time) ...push down on the front, middle of the seat while at the same time lifting from the back (where the seat belt locks come from in the gap)...
you should feel it come free after a little convincing.
then do the other side and lift the seat out.
at the bottom of the back rests are bolts on either side, undo these then push the back rests directly up (push into it a bit too)..they should slide off.
then unbolt the centre back rest now you have the access.
along the edge of the parcel shelf you will see plastic rivets, pull them out and you've done it.....if you want to competely take it out (which isnt neccessary just for puttin 6x9" spacers on) you'd need to also disconnect existing speaker wiring and the rear brake light (the one up against the windscreen, not the one on the boot,lol)
and that about does it...
*edit*..i knew someone would reply why i was writing all that..