You will need the Full Account permission to cancel. It bypasses no campus or organization limit: with more than one organization, a Full Account holder with any limit sees the subscription read-only.
The billing cycle starts on the day you upgrade to a paid plan and renews automatically on the same day every month, unless you are on the annual plan. You can cancel at any time from Account Settings.
To change your billing date, contact customer support. See How do I contact support?