Hey, there is a cross brace across the back that you can take off from the trunk side. It is metal and in front of the smooth plastic back on the back of the back seat, if I'm thinking back correctly (haha, back!). Then, on the inside, take out the plastic trim piece (one on each side) in the lower rear corners of your back door jams. I don't recall if you first remove the bottom piece of the door jam trim, then the rear corner piece. Underneath those trim pieces is a bolt that holds down the bottom left and bottom right corners of your rear seat cushion. Once those two bolts are removed, and the rear brace is out of the way, you can lift your rear seat cushion up, towards your rear window. There are three hooks on the seat cushion that go over three spots on the rear deck area. They are on each corner, near the seatbelt and one in the middle. When putting the seat cushion back on, be sure to flex it to properly hook into these spots.
As a bonus, take the head rest off of the passenger seat, scoot the seat all the way forward, into the glove box almost, then recline the seat all the way into the back seat and press it past the cushion and you will see you have a freaking cavern from the glove box all the way back to the trunk lid! You now have a sort of flat area you can lay down on with your head in the passenger seat and feet in the trunk. This is where I sleep when I go snowboarding! Also, your car is now a truck! The wife and I can load three doors with door jam, or 8' long boards or trim pieces in there and still close the trunk. We loaded 12' and 16' long trim pieces with them hanging out the trunk and a red flag tied on.
I know you're just putting on a seat cover, but before you put the cushion back in, be sure to lower that passenger seat the way I described and you'll see what I'm talking about. The space really is impressive.
We sometimes put the rear cushion back in, but don't put the brace, plastic rear cover, trim pieces or bolts back. So it just pops in and out as needed. Enjoy!
PS, welcome to the site.