We'd hate to see you go, but you can change your plan level or cancel your plan on your My Account page. You can cancel your plan by selecting the "Cancel Subscription" option—no hoops to jump through in the cancellation process.
If you need to stop or suspend your subscription temporarily, remember that downgrading to Free is always an option. This will preserve all of your settings and customizations, so if you want to return to Acuity in the future, all settings are restored. You can cancel and upgrade at any time, and there are no fees to cancel.
If you want to delete your account entirely that can be done by selecting the "Delete My Account" option on the My Account page after you've downgraded to the Free Plan (cancelling).