I just got married and want to change my son last name to my married name

Does your new husband want to adopt your son?

It will, to some extent, depend upon which state or country you are in, but in general a change of a minor's last name will require a court action. Permission of the child's father may be required.

Any question on law needs to include your general locale as laws vary by area.

A birth certificate is considered a legal document in most of the world. This means to legally change your son's name will probably require a court order as AK said. A court will very likely require that you get the child's father's permission for the change. Or at least show that you tried to get his permission if you can't find him.

If the father objects, I doubt if a court would agree. On the other hand, if your husband wants to adopt, the court may override the father's objections.

We need more details to help.

If the child's bio father will agree, there is no problem at all, get him to agree and go to court house and do a name change.

If the new husband wants to adopt, again, get the bio father's permission