You must first upgrade EMS to 7.0.3 or a later version before upgrading FortiClient from 7.0.2 or an earlier version.
FortiClient EMS supports direct upgrade from EMS 6.2, 6.4, and 7.0. To upgrade older EMS versions, follow the upgrade procedure outlined in FortiClient and FortiClient EMS Upgrade Paths.
With the endpoint security improvement feature, there are backward compatibility issues to consider while planning upgrades. See Recommended upgrade path.
FortiClient EMS does not support downgrading to previous EMS versions.