You need to conatct symantec support.They will be provide old sep package removal tool.
see brian and chetan comments same thread in sepm 12.1.5
https://www-secure.symantec.com/connect/forums/removal-old-sep-packages-end-point-protection-sbe
QuickStart Guide - Create and Manage Support Cases in SymWISE
http://www.symantec.com/docs/HOWTO31132
How to update a support case and upload diagnostic files with MySupport
http://www.symantec.com/docs/TECH71023
OR
Regional Support Telephone Numbers:
United States: https://support.broadcom.com (407-357-7600 from outside the United States)
Australia: 1300 365510 (+61 2 8220 7111 from outside Australia)
United Kingdom: +44 (0) 870 606 6000
Additional contact numbers: http://www.symantec.com/business/support/contact_techsupp_static.jsp
See below thread
https://www-secure.symantec.com/connect/forums/bsod-due-upgrade-sep-12153375000