Firstly remove the back seat.
This sounds easy in hindsight, but is hard to begin with.
1. The bottom section comes out first
The tab in the bottom left hand side of the pic is what is trying to be removed.
It sits about six inches in from the door, and requires a decent (re: LOT) of force backwards and upwards to get it out.
After sweat and tears (thankfully no blood) the seat lifts up, and out.
2. The back section comes out next, and needs 2 10mm bolts removed. This then also lifts out.
The parcel shelf is then removed by pulling it up to remove those little plastic annoying tabs, and pulled towards the front of the car to get around the rear windsheild wiper.
(In my case, the brake light wiring was cut, and later soldered, as it would disconect)
3. The new speaker can now replace the old
In this case, JBL 60RMS 6.5" 2 ways compared to National 8w 6".
4. Put parts back together in the reverese order to which they were pulled apart; parcel shelf, back section of seat, bottom of seat.
5. Now its done, and except for the listener, no ones the wiser;
Sorry about pic quality i used a video camera.
Feel free to ask qs