What the fu(k, no you dont.
I think if people on here that dont do it for a living, or havent done it before should be careful what they say!
jesse_r : Go to your local audio shop, they will be able to supply 6x9 spacers for about $35 for singles, $50 for doubles, carpeted. You may need singles or doubles, depends on the speaker.
Maybe have the factory speakers out before you go so they can suss out the best spacer
To take the speakers out, remove the horizontal part of the back seat by pulling up very hard. Now remove the verticle part, two 10mm (or 12mm, I forget) bolts either side. Now push it straight up, there are upward facing hooks holding it on.
Now the tray can be removed, its just clipped down.
Remove the factory speaker grilles (screwed onto the tray)
Remove the factory speakers and put it all back together.
Now, screw the speaker onto the spacer (outside the car)
Put the spacer and speaker into the hole, line it up so it looks straight
Go in the boot, pulling down on the magnet, or get a mate in the car to push down on the speaker, screw into the spacer from underneath. 2 or 3 screws is fine.
Extend the factory wiring making sure to get the phasing correct.
Remove the rear screen? pffft.