I am interested in changing my sons last name. He is 12 Yrs old and has one younger sibling already and another on the way. His father has had no contact including child support in 5 yrs. How can I change his name so that he has my married name?

All you have to do is call the local court house for your county or city, laws are different for each state on that, if you call them they can tell everything that you need to know.