Hi,
if the Manager is updated and the clients are properly connected to Manager, they automatically get the latest definitions.
There is a command "update content in the clients" but this is useless because the mechanism is the same, therefore, if the automatic deployment of updates does not work, the command will fail as well for sure.
Step by step troubleshooting:
1) is the Manager really updated? In the console of the Manager > admin > server > local site > "show liveupdate downloads", are the AV definitions updated?
2) are the clients properly connected to the Manager? in the client, double click on the yellow shield > help and support > troubleshooting, are you reading the IP or the hostname of your server in the field "server"?
Cheers,