Changing babies last name to his dads last name?😐

Em

My sons father had nothing to do with the pregnancy and refused to come to the hospital to see his son or sign the birth certificate until a dna test was done. A month later we got the dna test done and he’s been semi involved with his life since. He sends me $100 a week and sees him about once a month. He’s just NOW asking to get our sons last name changed to his last name and I feel like he’s trying to manipulate me? Please give me y’alls honest opinions on what I should do!