Changing hair color from dark brown/black to blonde?

Hey everyone, first post here.

Anyone know of a good way to turn dark hair into a blonde color? There are plenty of hair changing tutorials out on the net but going from dark to blonde seems much more difficult than other changes. I've tried experimenting with curves, then color selection but nothing seems to work. It always comes out looking unnatural. Here is the image I am working with:

http://www.just-whatever.com/wp-content/uploads/2007/07/lena_headey_01.jpg

Any help would be greatly appreciated.

I gave it a go, but as you said, unnatural look to it, THAT IS ALWAYS SO TOUGH.I suggest using a blonde wig image to replace it probably much easier and faster for me anyway lol