Serve a copy of the motion for modification and supporting affidavit on your former spouse. (info.legalzoom.com)
In this type of application you should obtain legal advice about who the necessary parties are and what to include in supporting affidavits to make sure relationship issues are addressed. (familycourt.gov.au)
The application in that action is available online, as are a number of supporting affidavits. (slaw.ca)