It is better to have the clients managed. If you have the clients as unmanged then all the clients will go to the internet to take the update uncessary wasting the bandwidth. if they are managed the SEPM will update it self and then inturn it wll update all the clients.
How to change a Symantec Endpoint Protection client from unmanaged to managed
1.Copy of the file Sylink.xml from the server from C:\Program Files\Symantec\Symantec Endpoint Protection Manager\data\outbox\agent\
2. On the client computer , click Start > Run, type smc -stop, and click OK.
3. Copy the Sylink.xml into the C:\Program Files\Symantec\Symantec Endpoint Protection folder, and replace any existing Sylink.xml file.
4. Click Start > Run, type smc -start, and click OK.