Visit https://www.actionnetwork.com/login using a desktop or mobile web browser.
Once you're logged in, hover and click on your avatar icon at the top right of the page to receive the drop-down menu. On the drop-down menu, select the Settings tab and it will populate the settings page which includes the Manage Subscription option, please select this tab.
Within the Manage Subscription page, you will be able to find the option to cancel below the Manage Plan section.