Photoshop cs3, changing hair color question, 15 points?

I am trying to change hair color from brunette to blond, I have looked at all the video's on youtube and every other place and have followed the directions exactly. After I have selected the hair and am trying to change the color, it just changes the color of the whole picture and on the hair the color doesn't really change. It makes it like a tiny bit lighter, but that just makes it really really grainy. 15 points