Qualified Medical Child Support Order. 1. Fill out a child support modification petition. 2.File the petition with the Family Court that most recently established your order. 3. Washington State's official mandatory pattern forms for child support modification can be found on the State Court website. A modification of a child support order may be requested if there has been a substantial change of circumstances since the order was entered. Child support orders may be reviewed and adjusted as follows. Administrative Review. Step 7: Fill out these forms and take to your hearing. Completed Form Name. What forms do I use to modify a motion for child support in Clark County, Las Vegas, Nevada?