You will need to take out the back seats and the back dashboard.
1) Pull out bottom portion of seats by pulling the two rings and lifting the seat up and out, pull the seatbelts through it.
2) Unscrew two screws in the lower corners of the upper portion, then pull down the armrest and pull off the backing portion (its velcroed in so just pull it off) and then undo the two screws there. You will then pull the back of the seat UP as far as it can go, then out forward. This is becuase the seat is hooked on by three hooks behind it, which when you replace it back, you will need to push it flush and down with these hooks.
3) Take out the three fuzzy screws on top of the rear dashboard. Then pop out the four plastic rivets (black) that are on the front (brownish) portion of the back dash.
4) Remove the brake light by pulling it towards you, then unplug the wire harness.
5) reach up underneath the back dash and push up pretty hard. You will feel rivets poping out. This is ok, there is five of them along the back of the board by the window. These will just snap back into place when you put it back.
6) Pull the dash cover up and down. You cannot take it out of the car becuase the seatbelts go through it so you just have to hang it there (unless you wanna unbolt the belts.
7) You got access to the speakers. Unscrew them and fuck with them at your liesure. You will also have to unplug the wire harness from the trunk side.
NOTE: The stock rear speakers are an OVERSIZED 6.5" or sometimes referred to as 6.5 plus size or 6.75...standard 6.5 requires a little playing around with so be careful what you buy.
8) Reverse the process when installing the shit back.