As strange as it might sound, the best way to shrink a fitted hat is to shower with the hat on your head. The steam from the shower will shrink the hat to fit your head perfectly. Generally, the best time to do this is right before you are done taking your shower. Then wear it outside until it dries and it will be a perfect fit. To find more information click here: http://www.baseball-fever.com/showthread.php?t=57894
To shrink a fitted hat first lightly dampen the hat all over with water. Place the hat into the dryer and check it on your head every minute. Keep drying it until it fits. Let it air dry the rest of the way.