In Photoshop (you may want to create a dupe of your image so you still have the original) go to Image>Adjustments>Desaturate, this will make the image B&W. Now go to Edit>Fade Desaturation, and once opened you can set the slider to whatever, the smaller the number, the more color or less desat to the image.
Robert
Learn more stuff @ Supershoots San Diego Smackdown, Feb 28-29 (almost sold out!)