Just login to your iwantmyname account, click on the domain you want to cancel, then on the dashboard page click cancel to the right of Next Billing.
If the renewal billing has been completed but the domain hasn't yet been renewed at the registry, we can cancel the renewal for you and process a refund.
To check that, look at Renewal Date on the domain's page in your dashboard to see if the date shown is fairly far in the future (e.g. if it's 2017 and the date shows 2018).
Login to your iwantmyname account and send us an authenticated request using our support form. Be sure to let us know which domain renewal to cancel.
We can then cancel renewal and refund the billing for you. Refunds will show up in your statement within 7 business days.
If the renewal has been billed AND the domain has been renewed at the registry, we are no longer able to process a refund. You now own the domain for another year, but you can set it to expire at the end of that year in your dashboard.