Changing Membership from Monthly to Yearly
It's easy to change from a monthly to an yearly membership.
You can do so at any time from your membership dashboard.
Look for the "Upgrade or change your subscription" link.
When changing to an yearly membership, you will receive a proration credit from between $0 to $15, based on how far into your current monthly plan you are when you make the change.
Have a look at the following video for a walkthrough on migrating to an annual membership.