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Latest Symantec version is SEPM 12.1 RU4 MP1a.
Latest release details are available here: http://bit.ly/m0vOJp
Upgrade process is very straightforward, refer the following article prior to start upgrade process.
SEP 11.x to SEP 12.1 Upgrade process graphical overview
https://www-secure.symantec.com/connect/articles/sep-11x-sep-121-upgrade-process-graphical-overview
After successfull SEPM upgrade use auto upgrade feature to upgrade existing SEP 11 RU7 clients.
For auto upgrade refer this article:https://www-secure.symantec.com/connect/articles/sepm-121-auto-upgrade
SEP 12.1 employs a side-by-side, replace on reboot installation strategy. Side-by-side means that new files are written to a new folder, referred to as a silo, isolated from the existing operational folder. Because the two versions are separated from each other, during a migration the older software is left running unchanged until the next reboot.
The primary benefit of side-by-side installation and replace on reboot is that the system continues to be protected by the existing software until the new version is in operation after the reboot.
This technique enables you to change the normal portion of the installation path during a migration, when applicable.