Interior rear panel.

Are you talking about the rear "Package" tray or commonly known as the rear speaker tray? That shelf that's behind the rear seat, correct?

In order to remove and replace it, you will need to remove the rear seat to get to it. The rear bottom seat needs to be pushed in on the bottom straight back and up at an angle to get over the locking mechanizm that's welded to the floor. Once the seat is removed and out of the car, you will se a pair of screws with large fender washers on them which are holding down a couple of metal bars that are integral to the upper back seat. Remove those screws and lift upward at an angle on the upper seat. It should slide on the metal and cardboard trunk divider and from there, you sould see the lip of the vinyl from the rear package tray glued to the metal trunk divider. Remove the old stuff and install the new package tray with some insulation and sound deading material and you just have to reverse these procedures and you should be good to go.

You might have to remove your sail panels but the new cardboard material is flexible enough that you should need to but I just wanted to let you know...