Hi I want to change my sons last name but don't know how? When I was 17 I gave him his dad's last name his dad has never been in his life and didn't even sign the birth certificate I really want to do this but don't know what to do I live in Miami Florida. PLEASE HELP.

Since a birth certificate is a legal document, you have to obtain a court order in your local family court to do this. You may be required to get the bio parent's agreement.

Contact the local Family Court for the procedure.