To cancel scheduled Payments in Blackbaud Grantmaking (GIFTS Online), you must open the Payment record, then choose Actions > Cancel. You will be prompted to amend the grant amount during the cancel process - depending on your workflow, you may wish to leave this alone or drop the grant amount by the amount of the cancelled payment.

Bear in mind that only Scheduled Payments can be Cancelled. If you have Paid payments you wish to "Cancel", you must instead Void them.