Can anyone offer some hair advice?

[pinkblink]

I have mid brown with a reddish shine (if that makes sense?) hair naturally, I box dye a dark brown. I want to take the colour out at the back underneath so I can put a nice bright colour in, so it will show when my hair is up, any advice on what to use to lighten my hair?
Thanks

This sort of idea, I didn't explain it well, not that it matters it's colour advice I need