For any adoption there are legalities. I would imagine since this is a relative it would be a lot easier but you still have certain legal avenues that must be followed.  It may be as simple as signing some papers to prove your legal status now with the child or as complicated as contacting both parents and getting them to sign the child to be adopted to you. Seek an attorney's advice.

I don't know the domestic laws in OH but it shouldn't be to difficult if you already have legal custody and neither bio parent has any involvement. Check with your local court house and see if they have free legal clinics or legal aid that can help you with the forms that you need. Here in CA, a lot of things like this can be done yourself.  If your local court house can't help you, call your local Bar Association and they may be able to set you up with a low cost visit with an attorney who can tell you what needs to be done.