You must file for a name change in the Circuit Court of the city or county that you reside in.
If you are Petitioning to change the name of your child, you will need consent from the other parent. If the other parent does not consent to the name change you may want to seek the help of an attorney.
You must provide a copy of your birth certificate and all documentation showing any previous name changes (i.e. divorce decree, name change order, etc.)