Well, I've never dyed me hair black...almost did, but I chickened out lol...but anyways, whatever you do DO NOT bleach you hair because it will ruin you hair. If it were me I would just let my hair grow out and then cut it because that's the safest / healthiest way, in my opinion, but if you're not planning on waiting a few weeks/ months for that then go to a hair salon and ask someone there because if you've never had balck in you hair you don't want to get it out of you hair alone because it's the worst to get out....my sister had clack hair and it didn't turn out well getting it out. But that's what I would do.
Good luck to you sweetie! :) Hope I was of some help.
<3 kt