Any easy ways to replace colors?

[smurfmidgetninja]

Ok well I have a friend that has Halo sprites for a webcomic they make and they want them recolored so she can have a sheet for each character from Red vs Blue. and I have been like just replacing the colors pixel by pixel but its taking an outrageously long time....so I was wondering is there an easy way in Adobe Photoshop to replace certain colors with another color or is there another program that would do this for me?

Edit: I don't have vip/gold so I only have one post so

@konidias: Thanks I will look that up on google and try it out.

@Butz: Hue/Saturation adjusts the levels of the whole image doesn't it? Therefore it would change ones I wouldn't want changed aswell.

KONIDIAS! I LOVE YOU! Seriously you rock! I owe you bigtime man