When upgrading your account or changing the billing term, credits and charges are prorated at the time of purchase. More specifically:
When upgrading your monthly account from one tier to another (i.e. monthly Basic to monthly Standard), a prorated credit for unused time from the lower account is applied.
When upgrading your annual account from one tier to another (i.e. annual Basic to annual Standard), a prorated credit for unused time from the lower account is applied.
When upgrading your account tier and changing your term from monthly to annual (i.e. monthly Basic to annual Standard), you will be billed for 11 months at the new rate plus however many days are remaining before your next billing date; a credit for unused time in the original tier will also be factored into the rate.
When changing your term but keeping your subscription tier the same (i.e. monthly Standard to annual Standard), your account will convert to the new term at the end of the period for which you have already paid.
You may purchase additional storage for your account as needed (Starter account holders may not take advantage of this option). All of our storage add-on options can be found by clicking Add Storage from your Account Info page. Storage add-ons range from an extra 10GB for $5/month, all the way up to 1TB for $1,000/year.
If you have purchased a storage add-on, you will see it reflected in the Additional Subscriptions section on your Account Info page.