How do you enhance and/or change the eye color?

Most of the time to highlight the eyes you increase the saturation and sharpen a little. There are many ways to change the color. The Color Replacement Brush in Photoshop is one very quick way. The use of a Hue/Sat adjustment layer is another. Painting with the Brush modde set to color also works plus many other ways.
Regards, Murray

There are heaps of tutorials on the net to help teach you how to change the eye color. check out the Tutorials section on this site there might be one there.

Have a look at http://www.lunacore.com/photoshop/tutorials/tut004.htm should be of use to you.

I really appreciate all the help!! Thanks everyone!