How can I cool off my tank? I've seen a hundred questions about heating it up, but what about the other way?

My tank pretty consistently reads just over 75 or 76, and my frogs are a bit sluggish. I've propped up their light and blocked a lot of it so that it doesn't shine bright on them, and it's only a 15 watt bulb to begin with. The room is pretty open, with plenty of air flow, and they've got mesh on a part of the top of their tank for ventilation.

I'm not even positive this is a problem. Some sites say they can be comfortable up to 80 degrees. I don't really want to stress them if I don't have to of course. I'm just worried that the problem will become even more significant once summer rolls around and it's ACTUALLY hot around here.

Any ideas?