Removing Pool Stairs From In Ground Pool
There's a metal tube set in the deck that the stairs drop into, the bolts push a metal wedge against the stairs to keep them in place. Your problem is most likely bits of sand/dirt/stone dust have gotten in there and are acting as a bunch of tiny wedges. Hours of sunlight can cause the stairs to expand slightly aggravating the situation.

A good first step is running a hose or dumping a couple of buckets of water from the pool over the connectors. The water will solve any heat problems while hopefully flushing enough junk out of the hole to free the stairs.

If that doesn't work then tapping on the stairs to dislodge or crush the trapped grits should. You don't want to use a hammer though, because it risks marring the finish. Use a rubber mallet if you have one, or a block of wood between the hammer and stairs.

A short length of 2x4 works well if you have one. You're a lot less likely to mar the finish tapping on the stairs with that than a hammer. As an added bonus if the tapping doesn't work you can slip it beneath the curves at the top and jerk straight up.

FYI the bolts are threaded into pawls which compress against the stairs when you tighten the bolts. After removing the stairs you'll want to thread the bolts back into the metal piece which is loose in the hole so you can put the stairs back in the spring.