Most Helpful Girl
I'm not an expert on coloring hair, but I would say that in your situation, it would be best to go to a professional. Since you're starting out with very dark hair, the effects of bleach will be quite pronounced, and any mishap will likely be more noticeable than it would be if you were starting with a lighter hair color. If you're determined to do it yourself, I would suggest leaving it on for a VERY short amount of time (look at the instructions on the package and go from there) and then bleaching again if the results aren't light enough. Also, I believe the color you end up with might be affected by the tones that are already present in your hair.