Unless otherwise agreed upon, all subscriptions are month-to-month and can be cancelled anytime.
To cancel a subscription (or to make any material changes) you must be a key contact for the organization with an active user account. Cancellations must be received before the 25th of the month to be canceled in the current month.
You typically have several options short-of cancellation. Before completely terminating your service, it is advised to understand your various options here.
If you know you want to cancel, you can proceed directly to the cancellation form here.