Supplemental Petition for Modification of Child Support. Form Number 12.905(b).Either parent can file their own petition in circuit court to change (modify) a support order. This form should be used when you are asking the court to change a current court-ordered child support obligation. Below are some of the Florida Supreme Court approved child support forms in Florida. Obtain the Necessary Forms: Contact your local family court or child support agency to obtain the required forms for requesting a modification of child support. However, in general, if you want to modify support you must file a Supplemental Petition to Modify Child Support. The first step is to request the child support change with the family court that first approved the order. 1. Obtain the form and guidelines for modification. This video provides guidance on filling out the forms required for Modification of Support or Parenting Plan.