Cancelling your subscription means that when your current license expires (1 year from purchase), you will no longer receive automatic updates and priority support.
If you still wish to cancel your recurring subscription, you can do so by following these steps. I will use WP School Calendar as an example, but all plugins use the same method (just the settings page is different).
First, navigate to your WordPress admin area.
Go to the plugin account page. In this example: School Calendar > Account.
Click Cancel Subscription.
Your cancellation will be confirmed and you will be notified of your expiration date. The plugin will still work as normal after that date and you may be prompted to upgrade your license at the time of renewal.