Name Changing

I don't know if this is where I need to post this so I apologize in advance! My sister in law adopted her son 6-7 years ago from a cousin. She didn't know to have his last name changed, although I would of thought the attorney who handled the adoption would have sought to do that... Anyway, now that he is in school, he wants to put the name he grew up with, my sister in laws, but his teacher is insisting he use the name on his birth certificate, of which he didn't have a clue. I will be helping her to file to have the name changed and during my research, I have only found issues involving the other parent's consent or a court order. Does anyone know where I can look for simply a name change? Thank you so much!