The Subscription Plan section tells you your current plan level - e.g., if you have a free account that is ad-supported, or if you have an upgraded subscription plan. Your subscription plan will also tell you if your account is set up for auto-renewal if you have added the Self-Book feature to your account, how many Calendars your account has, and if you have added any Expansion Packs to your account.

If you have a paid account and you access your Account Settings, you have the option of changing your subscription plan from paying monthly to a yearly subscription. Follow the directions in the image below to do this: