• FSSO- upgrade to 5.0.0330.

1. backup the agent config
2. backup the VM
3. Run installer

Hello ​@Nofal ,

Adding to what ​@AEK said, 

Since the process of upgrading the DC agent involves removing the DC agent from the DC and then reinstalling it, it will cause an interruption for the users.

Referencing Step 6 - https://community.fortinet.com/t5/FortiGate/Technical-Tip-Upgrading-FSSO-Agents/ta-p/191906

You may try to upgrade the DC agents one or couple of them at the same time, to limit the interruption for the users. However, if a machine has a logon event on a particular DC and that DC agent is being upgraded, it may cause an interruption for those user(s). I highly suggest you to make these changes during a maintenance window to avoid network issues during production time.