Just grab the front of the seat and pull upward... it is held in place by two spring clips at the front edge. It'll just pull up and out.

The rear side bolsters are held in place by two hooks; one at the top, and one near the bottom. The bottom hook needs to be freed first. Push the bolster in and down far enough so that the bottom hook is free... you will then be able to pull the bottom out. Once the bottom is free, the top hook can be lifted out.