[Question] Color 'Map'?

[worldslayer]

So I am taking a 16 bit color image. What i need to do is take all 16 colors and replace them with other colors.

Is there a way to do this without having to use the eye dropper, take a color, fill in the color I want to replace, repeat 15 more times? I really am looking for something a bit less time consuming and a bit easier on my eyes since the greens can get pretty close.

I have CS3, and to be honest idk how to edit the pallet colors :S

+REP to anyone who can help