Qualified Medical Child Support Order. To file such a motion, you generally need to explain the change in circumstances that have taken place which warrant changing the current support order.This document is a sample form letter designed for individuals seeking a downward modification of their child support obligations. These forms and instructions are available in the General Clerk's Office, Room 108, in the Nassau County. This Easy Form helps you ask the court to increase or decrease your current child support order. This is called child support modification. Form: Petition for Modification of Child Support. First blank: Your name. 1. Fill out a child support modification petition. 2. File the petition with the Family Court that most recently established your order.