We email renewal reminders 30, 14, 7 and 1 day before your domain expires, and again 3 days after if it is still unrenewed.
Renewals are invoiced to your client area and paid with the card on your account. To check or change your card, open Billing → Payment Methods.
You can also renew early at any time: open Domains → My Domains, choose the domain and select Renew.