Order (Relief from Support Payments and Commitment). PDF. 4-16. Notice of Motion To Quash, Fix or Modify Conditions of A Child Support Subpoena.1. Fill out a child support modification petition. 2. File the petition with the Family Court that most recently established your order. 3. 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. Step 1: Fill out your court forms. Fill out the following starting forms: â—‹ Petition to Modify the Parent-Child Relationship. The process for filing a child support adjustment in Texas starts with completing and filing a Petition to Modify the ParentChild Relationship. If you would like to change a child support or custody order that resulted from a SAPCR, you will need to file with the court for a modification.