There should be a bleeder bolt on the clutch slave cylinder.

Attach a plastic tube (preferably with a spring loaded ball bearing valve) to the bleeder bolt.
Put the end of the tube in a small (1 or 2 cup) container that's not affected by brake fluid.
Open the bleeder bolt about a quarter turn.
If you have the tube with the ball-bearing valve, pump the clutch pedal 3 or 4 times.
If you just have a plain old tube, you'll need a second person.
Open bleeder bolt a quarter turn, Have 2nd person press the clutch pedal to the floor and hold it. Close the bleeder bolt. Release clutch pedal. Repeat 3 or 4 times.

If the fluid isn't clear, repeat until it is. Topping off the clutch master cylinder as necessary.
If bleeding the clutch doesn't fix the problem, it could be a bad seal in either the master or slave cylinder (look for signs of leaking brake fluid)