Hi,
I would suggest to go ahead with Manual uninstallation for SEP 12.x and Keeping the usage of CleanWipe as the Last Option.
Incase, you are want to uninstall SEP 12.x, Uninstall from Add / Remove Programs
OR
Use the Manual Uninstallation Steps.
Manual uninstallation documents for Symantec Endpoint Protection
Incase, you need the CleanWipe, I would suggest open a web case (Faster and Easier Option)
You can log a case on web portal to receive tool.
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