You'll need some 6 pointed and 12 pointed star drives (torx?) can't remember the sizes.
There's a small one on the middle hinge for the upright, accessed from the boot and found under a plastic cover. Undo this and then pull off the metal bracket to release. Wiggle the upright's pins out of their slots in the sides of the car.
Then, you'll have to undo the bolt for the middle seatbelt, tricky to get at, but you'll see it.
Base just pulls out with a bit of a twist.