You do need to take out the seat to take it out. I just took mine out so its still fresh in my mind on how to do it.
1-To take out the bottom seat of the car just pull up, there are 2 hook holding it down, both of them are in front, one on the left side one on the right side. The bottom seat come off as an whole one part.
2-To take out the back part you must take out the passenger side first. To open the passenger side, from the trunk on the right find a wired hook hidden inside the side pannel of the top right. Once you pull it the passenger seat should come down. (not many people know the passenger side fold down)

Once the back is folded there should be 2 screws holding the seat.
3-Once the passenger seat is taken out you must unbolt part of the rear driver side seat to take out the sub. There should be 3 screws that hold the sub box to the car. Unbolt it and take it out.