Go thorugh Release & fix notes for SEP 12.1 RU1 (12.1.1000.157):
http://www.symantec.com/docs/TECH174565
Upgrading or migrating to Symantec Endpoint Protection 12.1.1000 (RU1)
http://bit.ly/rC916P
Migration paths
Symantec Endpoint Protection 12.1.1000.157 (RU1) can migrate seamlessly over the following:
Symantec Endpoint Protection 12.1.671.4971 (RTM)
Migration detects and migrates installations of the following Symantec legacy virus protection software:
• Symantec AntiVirus Corporate Edition 9.x and 10.x.
• Symantec Client Security 2.x and 3.x
• Symantec Endpoint Protection Small Business Edition 12.0
• Symantec Endpoint Protection 11.x
• Symantec Sygate Enterprise Protection *
• Symantec AntiVirus for Mac *