I haven't seen or used the PRS-13, but it looks similar to all of Parks professional stands. It should be a simple as loosening the bolt on top, pulling the bike clamp straight out, and pulling straight up on the bolt assembly. Attached to the bolt are two wedge blocks; these are what tighten against the bike clamp's shaft to keep it from rotating. If it won't hold the bike in the desired position, I would grease the bolt, and make sure there is no (or very very little) grease on the two wedge blocks.