I did this once. I bought powdered on scalp hair bleach, a high quality shampoo and conditioner (I bought Joico Moisturizing Treatment) and mixed per directions on the bleach packet. I added three tablespoons of shampoo and three tablespoons of conditioner. You may more than likely see it turning very interesting shades of red, then orange and eventually blondish. That's because we're removing all the dark layers first, what's left is red before it turns blonde. I also wrapped it in plastic wrap and zapped it with the hair dryer for about 20 minutes. Once my hair reached the right stage of lightness, I rinsed the bleach from the hair. I shampooed and used the moisturing treament heavily and wrapped it again in plastic wrap and left it in for a couple of hoursl. Afterwards, rinse it and color it using a toner or something mild.
Good Luck!