We email renewal reminders to the email address on your account before the domain expires, and an invoice is created ahead of the expiry date.
To renew yourself, sign in at hostripples.com/secure, open Domains > My Domains, select the domain and choose Renew. You can also turn on auto-renew for the domain so the renewal invoice is raised automatically each year.
Please renew before the expiry date. After it, the domain stops working, and for many extensions a late restore costs extra.