last name change?

When my son was born I put my ex's/ baby daddy's last name in his birth certificate. Well his dad did some pretty bad stuff ( don't want to get into it) and is in jail now. I want my son to know his dad and stuff without him meeting him if that makes sense, but I don't think he should have his last name. I want to get his last name changed to James which is my last name. My ex doesn't get to be in my sons life anymore so why should he have his last name? Any advice on what I should do? My sons name would be