It's not easy to describe but I'll point you in the right direction.

You'll need to fold down your back seat.
On a 4dr, you have to remove the side bolsters. Not sure how to do it on a coupe.
Then you need to remove the enter plastic rear deck.
There are three white plastic clip/pins which must be pop up from inside the trunk. This releases part of what's holding the back deck on. It's easy to confuse the other white plastic pins of other parts. (told ya it's hard to describe)
The rear deck is then held by several white pins that the deck is snapped onto. To release, pull the deck towards the front of the car to pop all the snaps.

Once the deck is off, it becomes obvious how to change the 6x9's.

Yes, you MUST remove the rear deck.