1993 Honda Civic Honda Civic 93 Cluth Problem

There is something wrong with my clutch. When I first start the engine, everything works fine until the car gets more heated up, and then the clutch starts slipping. Not that the clutch only slips when it's warm, but when it gets hot and you come to a stop, it will not shift into gear.

What does this kind of problem call for?

So far, I've only replaced the clutch because I thought that was out.