If it is like the '03, unfold the seat to the upright position. The seat will be bolted to the floor on 2 front legs and on each side in the rear under the seat. The '03 seat has 1 bolt in each front leg, 14mm and 2 bolts on each side in the rear also 14mm. Unbolt the front legs first, fold the seat flat and stand it up, then unbolt the rear legs. I'd go check to see if my '12 is like my '03 except I have 450 lbs of pool salt in it right now.
<edit> Rereading your post you want to remove just the seat back? I'm not sure you can.