Hello,
As suggested above - you may need to Migrate to the Latest version of Symantec Endpoint Protection 12.1.2015 and above for Windows 8.
Currently Latest version is Symantec Endpoint Protection 12.1.3001
In your case, you can keep the same license and migrate from Symantec Endpoint Protection 12.0 Small Business Edition to Symantec Endpoint Protection 12.1.x Small Business Edition.
Check these Articles:
Supported upgrade and migration paths to Symantec Endpoint Protection 12.1.x
http://www.symantec.com/docs/TECH198599
Supported Upgrade paths to Symantec Endpoint Protection 12.1
https://www-secure.symantec.com/connect/articles/upgrade-paths-sep-121amber
Upgrade process graphical overview: Small Business Edition 12.0 to Small Business Edition 12.1 RU3 version
https://www-secure.symantec.com/connect/articles/upgrade-process-graphical-overview-small-business-edition-120-small-business-edition-121-ru
Upgrading or migrating to Symantec Endpoint Protection 12.1.3 (RU3)
http://www.symantec.com/docs/TECH206823
Hope that helps!!