Hello,
There are a number of methods -
1) SEPM
2) Group Update Providers
3) Liveupdate (Internet)
4) Liveupdate Administrator
5) Manually Update SEPM and SEP client via .jdb and Intelligent updater.
6) Third Party Distribution Tools.
Check these Articles:
How to update virus definitions and other content with Symantec Endpoint Protection and Symantec Network Access Control
http://www.symantec.com/docs/TECH102467
How to update definitions for Symantec Endpoint Protection using the Intelligent Updater
http://www.symantec.com/docs/TECH102606
Hope that helps!!