1. Go to http://cloud.fontagent.com/FAServer
2. Log in using your admin email address and password.
3. Select the Machines tab on the left side. This will show you all of the machines that have registered FontAgent 8 (and FontAgent 7). The Sync column just means that machine is sharing fonts and can be ignored in this case. But what might help is to click on the "V8" column header to sort the rows. One other tip: you might look at the Date column, which shows you when the machine was registered—you can use it to look at old registrations to determine if they need to be removed.
4. To remove a machine's activation, click the Delete button on the far right in the row that corresponds to the machine you want to remove. If you accidentally remove the wrong machine, that user can easily re-register their installation of FontAgent. Deleting a machine's activation will not delete the users fonts, it will simply require that they re-register FontAgent.