If a customer is on a payment plan or monthly billing cycle you can manage their installments in multiple ways on the customer's order page, by finding these button below the Monthly Billings/Payment Plan Schedule:
Change the date an installment is scheduled to be charged to a future date.
Change the amount of an installment.
Cancel the scheduled payment.
Refund (at the bottom of the page)
Click this red button to create a partial or full refund to the customer.
Monthly Billing Ex.
Payment Plan Ex.