I am the biological father and I am on the bith cert. my son is 5 and does not have my last name. Can I change his alt name to mine? Do I need my ex's permission? (in the state of nh)

First, please pay more attention to posting guidelines. There is a sticky note at the top of the Children forum that refers legal questions to this forum.

A birth certificate is a legal document and requires a court order to change. The court is going to want both parent's approval to make a change.

I am not asking to change the birth cert. I am asking if I need his mother's permission to change his last name.

I am not asking to change the birth cert. i am asking if i need his mother's permission to change his last name.

Umm changing his name MEANS changing the birth certificate!