Go to "Manage > Invoices". Set the proper filters (e.g. 'Paid payment status', for all programs in the LIVE program state')
Click 'Bulk Invoice Adjustment'. Choose the amount you want to add to these parents' invoices. Choose to notify Invoice owners by email (this option is selected by default). You have the option to add a message (e.g. "2nd Installment due Nov. 15th").
- No action will be taken on invoices in 'void' or 'refund' status.
- If you wish to issue a partial refund or undo the latest payment installment that you have invoiced, be sure to 'Change the Amount Billed' by -$X (e.g. if you want to un-invoice a $250 payment installment, click to 'Change the Amount Billed' by -$250). DO NOT void the invoice, because it will void/refund the entire invoice, including every installment.