Changing sons last name

Ha

Does anybody know the process for changing my sons last name??? I dont care what it costs. Hes 2, his Bio dad hardly ever sees him(only does like 1 day a months for like 2 hours IF that. My husband, myself and our daughter have the same last name and I kind of want to change my sons soon. I do NOT have a court agreement with his dad and he has NOT agreed to establishing paternity.