He should speak to a family lawyer. I expect he'll be told to raise the issue of paternity in his divorce case. The divorce court can declare that he's not the father, such that he loses any visitation or custody rights but doesn't have to pay support. Note, that doesn't always happen.

If mom wants to change the child's name, and he consents, it's possible. If he wants his name removed from the birth certificate his best bet is to convince the biological father to petition for a finding of paternity and to cooperate with that process.