I believe you go to your dashboard and then the shopping cart is the icon for the store. There should be a button there to request a refund:
Just in case you’re not happy with your upgrade we offer a limited refund on newly purchased upgrades.
New domain registrations will be refunded if requested within 2 days.
Domain renewals are non-refundable.
Most other upgrades can be fully refunded within 30 days of purchase.
You can use the "Cancel and Refund" button if available or Contact support if you want to request a refund.