When you want to remove access for a user, you can deactivate them to avoid being charged for the subscription while still retaining access to the historical activity, such as tasks and notes.
To deactivate a user, just go to Settings > Organization and click the Deactivate button
If you are on a monthly plan, it will automatically reduce the number of subscriptions.
(Please note that while the downgrade happens immediately, it can sometimes take a while for the settings page to reflect this. We're working on a fix for this, but if you are at all concerned, just reach out to us and we'll confirm it for you.)