Use the following steps to disable or cancel a payment plan instance for a customer (note that Edit Payment Plan Instance permission is required to disable a payment plan instance):
Search for the customer, invoice, or license associated with the payment plan instance.
Scroll down to the Payment Plans section of the page.
Click the Disable link on the right (this will only appear for active payment plan instances)
Optionally append anything to the notes on the payment plan instance regarding the cancellation.
Click the Disable button.
The payment plan instance will be set to Inactive status, the next payment date will be cleared, and any users with Notify Final Payment Plan Declines permission will be notified by email of the cancellation.