Lightening Dark Hair
A: VERY CAREFULLY. As I've said before, lightening the color of the hair requires dispersing the pigments that exist within the hair shaft and is a process that can be harsh to the hair.
This is not something you should do yourself. There is too much risk of damage to the hair if not monitored very closely. There is also the issue of whether your hair is of sufficient condition to withstand such a dramatic color change.
You should seek the services of a salon professional to make this type of color change. He or she is trained to make a qualified assessment of your hair's suitability for color and can determine the best method to use to achieve the results you want, provided it is possible to do so.
If you do visit your salon for this procedure, and it gets done, PLEASE be sure to follow your stylist's hair care instructions to the letter. You should consider your hair to be the most fragile part of your body once it has been lightened from one extreme to the other.
This means using extreme caution with heat styling appliances and hair dryers, avoiding styling products containing alcohol, and drying the hair with a towel in the most gentle manner possible (pressing and squeezing to blot away excess moisture).
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See also:
How bleaching hair works
Hair color levels and peroxide developer
Where does the color go when you bleach dark hair?
How can I remove bleach from my hair?