Change My Child's Last Name

My question involves name change laws in the State of: TN and NH

I have a 7-year-old son from a previous relationship. I was never married to my son's father, he's never had custody, and my child has my maiden name for his last name. His father does pay child support to me through the state of NH. I now live in TN and I have since married and had a child with my husband. We would like to change my son's name to our name. I know we need to get a lawyer but do we need to involve my son's father in the proceedings ? What else do we need to do?

Yes, Dad will need to be at least notified.

Since kiddo has had your name (and not Dad's) since birth, you have a better chance than most of getting the name changed.