These forms and instructions are available in the General Clerk's Office, Room 108, in the Nassau County. Support Modification Packet Forms and Instructions, pdf document.1. Fill out a child support modification petition. 2. File the petition with the Family Court that most recently established your order. 3. A list of Filing Fees can be found HERE. Child Support Forms. The aboved marked forms are available to purchase in the Family Law Clerk of Courts office located in room 2474. Make 2 copies of each form and take all of them to the Clerk of Courts and ask the clerk to stamp all of them. Org - (select) – Self Help, Family Law Forms for the forms. 2. Visit the family court where your court order was issued and complete a Support Petition for Modification form (also known as Form 4-11).