I'm naturally blonde (and currently and will forever be black), and I've gone from black to light blonde lots of times. What you can do is... Scrub it out with dishsoap first. Then you'll need to get color stripper. The best IMO is in a white box with three very 80s looking women on the front. Other good ones are Wellalite (the oil based kind) from Sallys, or Manic Panic's Flashlightening bleach kit (works very well but can potentially be very damaging -- use caution!). It would be hard to tell you what volume developer to use...40 will work, but can be extremely damaging. If your hair is in good condition, I'd use 30 very carefully, checking your hair for breakage frequently during the process. You'll have to bleach it out light enough to whatever you want to get back to. You'll then need a purple toner, which will counteract all the yellow/brassy color that you'll be left with. After that, you can dye over it with whatever you want (though you will probably not be able to go very light blonde...you'll still have some orange left most likely).
I highly recommend getting a good conditioner (L'Oreal nourishing creme from Sally's works miracles) and some jojoba oil to treat your ends with. You'll probably need a trim after the bleaching, too.
Personally, I love black hair. I've had it for a long time and I can't imagine going back to my natural blonde. I use henna and indigo for it and it has left my hair in awesome condition.
Good luck! Feel free to PM me...I've been dying my own hair every color in the rainbow for about 10 years now.