For payment processors Stripe, Litle, Paypal or SagePay, you can use myLab to issue a refund for an order paid by credit card. Find the order (Orders > search or track) and click Issue Refund.
NOTE: If you use Authorize.net you will need to log into their admin site in order to process a refund. We will be adding Authorize.net refund functionality to myLab in early 2015.