Your agreement can only be changed by making a formal written agreement, or by going to court. Your court order may be administratively recalculated by the Child Support Recalculation Service, or changed by going to court.
If you wish to change your order by going to court on your own, you can use a self-help kit. Self-help kits contain forms and instructions for changing support orders. Kits are available, free of charge, from the Family Law Information Centre. You may also find and create your court forms by visiting PLEA's family law website.