I replaced mine last weekend with a set of Audiobahn plates I had lying around. I used the 1/4" drive ratchet with the 1/4" socket and a torx bit. Be sure to hold a finger on the bit when using it so it doesn't fall under the carpeted rear deck. It helps to let the seat you aren't sitting in down so you can reach under the speaker. After the screws were out I twisted the speaker around so it would drop through the rear deck. I was scared of scratching my tint. Then I went through the trunk and pulled the plugs off. I also flipped the plastic clips over so my new speakers mount from underneath. I used the small blue clamshell splices for wiring. Works great so far, but I need to recheck the screws to see if they are working their way out since I flipped them.
I have had great service in the past from Crutchfield, but I already had speakers and the price for adapters is high if you don't buy the speakers.
The plates made a world of difference in the highs in the rear. I was surprised at how cheap the rears were compared to the pictures of the other speakers in the car. I am now debating on the door subs and bridging the amps. I have been looking in the forums for weeks for the instructions and have yet to find them. I find a lot of mentions about bridging, but no instructions. Same with speaker choices. Kicker fits right in, but several others are mentioned but not by name.
No one mentions replacing the subs in the trunk either.
