If a judge agrees, they will give you a court order that states your new legal name. To change your legal ID documents, you will need at least one certified copy of your Decree.The clerk can get you a certified copy. The first step in legally changing your name is to file a Petition for Name Change with the California court in the county where you reside. Send the completed Affidavit form to the State Office of Vital Records. Address: California Department of Public Health. Legal name change in Alameda County. Top-rated Alameda County name change service, we help with petition forms and court filings. • Complete the new deed. • Grantor signature needs to be notarized.