Here is some usefull articles
Upgrading or migrating to Symantec Endpoint Protection 12.1.5 (RU5)
http://www.symantec.com/business/support/index?page=content&id=TECH224034
see chetan articles
Upgrade Overview to SEP 12.1 Release Update 5 (12.1.5337.5000)
https://www-secure.symantec.com/connect/articles/upgrade-overview-sep-121-release-update-5-12153375000