To stop the free user access to the lead / customer, in the lead on the lower right, click "Participants" to select the desired participant, and click on the red icon next to the user name). Thus, we close the user's access to the entity.
You can also delete a free user in the "Settings" - "Users" section. It should be noted the user ticked. Then the "Delete" item will appear. When you delete a free user, access to all lead / customer and the account as a whole will be terminated immediately.