Is it a hatch or sedan?

If it's a hatch, the grille is part of a larger plastic piece. Look at the sides of it, there should be one screw facing the back of the car and one facing the middle of the hatch. You also will need to flip down the seat, there is a screw on the front of that panel.

Pull the panel off, and you have a 6.5" speaker that is wired directly to the car, no harness. There's plenty of depth so assuming the JL's you're looking at fit a standard 6.5" opening then you should be fine.