Which piece are you removing, the piece in the hatch, or the piece by the rear seat?
If its the hatch piece, its not too hard. Start off by removing the floor piece.
First, remove the side trim by the hatch opening; should be held in with 2 plastic screws and expansion sleeves.
That will expose a plastic plug holding the felt to the car. Pull that out; its tight. There is another one of these plugs up front, holding the felt thing to the rear passenger trim piece to the body. Remove that too.
Loosen the upper trim piece, which houses the rear sholder belts. Its held in by 4 screws. The felt piece should come out then with some wiggling. If you need more room, the upper trim piece pops out some, since its also held in by a pop-tab.
Reinstall will be the reverse of this, but you might have to remove the bottom hatch trim to get the side pieces back on. Its held on by 6 plastic screws and expansion sleeves.
Also, pay attention to how pieces layer, like which piece is on top of which. That always threw me for a loop the first time.
The trim piece, you know where the speaker is, where the mini storage space on a ZX3 is. I know how to take apart my hatch but not that, I want to know about the part where the rear seats are, not the rear hatch piece, that won't allow me to gain access to the rear 1/4 panel.
For that piece you have to remove the two pegs in the back of the panel and then it just pops out. I would recomend removing the seatbelt pillar piece to make removal of the speaker piece a little easier. When you pull the panel out, pull up first and the towards the front of the vehicle. Reinstall in the same fashion. Peace