Step 1: Fill out your court forms. Fill out the following starting forms: â—‹ Petition to Modify the Parent-Child Relationship.Here's what to expect when you request for a modification of your child support order. Click here to learn the steps in the modification journey. This document is a sample form letter designed for individuals seeking a downward modification of their child support obligations. All child support forms are categorized and linked below as downloadable files. Select the category you need to see the corresponding forms. Download a free child support modification form to propose changes to a current child support agreement. Available in PDF or Word format. This guide includes forms and instructions for a letter and affidavit to request that the court register an out-of-state custody order in Texas.