Upgrading from previous EMS versions
FortiClient EMS supports upgrading from previous EMS versions as outlined in FortiClient and FortiClient EMS Upgrade Paths. After upgrading from FortiClient EMS 6.0, you cannot make changes to the FortiClient Enterprise Management Server license. Increasing the number of managed endpoints requires you to purchase a new FortiClient Security Fabric Agent license.
Downgrading to previous versions
Downgrading FortiClient EMS 6.2.1 to previous EMS versions is not supported.