I am 16 and I have had contact with my birth mother and it was an open adoption, but I need to know what I have to do to move back with her, and if I can do it since I am only 16?

What you have to do is wait until you are 18. Even in an open adoption, your birth mother gave up her rights. She has no legal rights where you are concerned. Your adoptive parents have those rights.

Why do you want do this?

I can't imagine what it must feel like to be in this situation, but I still wonder: have you stayed with her some weekends or vacations? Is she in your school district, and what about friends at school? How does she feel, and is she able to feed and clothe you, and be there when you get home?
These are practical matters to think about aside from your desire to actually move in with her now instead of in 2 years.

Legally, the person who gave up her rights to be your mother is no longer legally your mother, She has no legal rights and could not even visit if your adoptive family objects.

There is no way for her to get any legal standing in this

GV70 finds this helpful : That's why I am against this kind of adoption.The BM may play "Good Mommy" without any obligations.

And some birthmothers DON'T do this. Studies have shown that open adoptions are actually BETTER for everyone involved--and most birthparents know that being involved in their child's life is not the same as being their legal parent.

I'm betting the OP hasn't even talked to her birthmother about this--because *I* would have responded to my child that she needs to stay with her adoptive parents.

Don't lump us all together. Most of us know better than to cross that line.