Hi,
Thank you for posting in Symantec community.
I would be glad to answer your query.
On January 5th, 2015, Symantec Endpoint Protection version 11.0.x will reach end of support life. Virus definitions and security updates will cease to be published to LiveUpdate and general support for the product will no longer be provided.
The initial end of support life date was originally scheduled for January 5th, 2014. All customers were provided a complimentary extention. No further extentions will be provided.
It's strongly recommended to upgrade to SEP 12.1 , RU5 is the latest release.
Total how many client machines are in the network?
To upgrade an unmanaged client, you can overinstall with a newer build of Symantec Endpoint Protection.
After installation completes, you must reboot the computer.
No unmanaged clients require the manual installation of a license file. However, to enable the submission of reputation data from an unmanaged Windows client, you must install a paid license on the unmanaged client
Best practices for upgrading to the latest version of Endpoint Protection 12.1
http://www.symantec.com/docs/TECH163700
FAQ: Upgrading Symantec Endpoint Protection 11.x to version 12.1.x
http://www.symantec.com/docs/TECH207274