Mimi, it really matters at the moment who you go to. You will need to find a really experienced stylist who will advise you honestly about the end results of putting more colour on your hair. It'll all down to your type and conditon of yout hair currently. Its a heavy job lifting dark brown hair to blonde, especially if it's already coloured beneath the brown . I'm a hairdresser so I know the pitfalls of sucha dramatic change. At worst you could find your hair breaking off. At best, you'll probably be left with hair that needs loads of TLC as it is bound to be fragile with all the colourant you've had on it. Think very carefully and have utmost confidence in whom you chose to do this type of work on your hair. Good luck