To enable Auto Renew for a domain name do the following:
1) First login to your client area at http://www.hostiname.us/, then go to My Domains --> Manage --> Enable Auto Renew (note, this is enabled by default)
2) Check that you have a valid card on file and if not add one. To do this go to Billing --> Add / Update A Credit Card
3) Set your default payment method to Card, if not already, by going to My Details --> Payment Method (select Credit Card from dropdown box)
To disable Auto Renew simply repeat step 1 and select Disable Auto Renew
