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My rear leather seats have a white plastic C channel that clips to the frame. I imagine the cloth is the same. Pull the white plastic part away from the seat and rotate it so it doesn't hook back on as you move to the next one.
Same way, infact I have a replacement leather and foam sitting in my office for mine. I am not sure about the upper, but it may have a zipper or lacing to close the bottom. Once you separate the top and seat bottom, it should self expanitory.