To renew your domain name, visit:
and click on any link to "Renew" a domain name.
Renewal pricing per year is also shown on that page.
To manage your domain name registration, visit:
Follow the link on that page to "Manage Your Domain" --
you will be linked to a control panel for managing your domain name registration.
(This is different from the cPanel control panel -- see the Web Hosting section of this knowledgebase.)