Hello,
Why not just upgrade the SEPM and then use the Autoupgrade Feature??
http://www.symantec.com/business/support/index?page=content&id=TECH96789
In case you want to use the script, for removing previous version of Symantec products you can use the SEPprep tool:
http://www.symantec.com/business/support/index?pag...
...otherwise please note if you are upgrading to newer SEP version - uninstalling of previous 11.x client is not necessary. Installer can without issue migrate from previous versions.
AFAIK, if the uninstall password is configured, there is no way to uninstall SEP silently. Therefore, if you ever need to perform a mass uninstall by script/GPO, you will first have to remove the password protection. If you're looking to do a uninstall on a specific client remotely then you'll need to move that client to a specialised group where the password protection is disabled.
The closest thing I can find as a reference is the article below (This is for v11):\
http://www.symantec.com/docs/TECH105827
More general MSI uninstall information can be fond here:
http://www.symantec.com/docs/TECH102470
Secondly, check these Articles below:
Methods for uninstalling Symantec Endpoint Protection
http://www.symantec.com/docs/TECH184988
To Uninstalling client software with Active Directory Group Policy Object:
http://www.symantec.com/docs/HOWTO55432
Take a glance at these 3 links and let me know if this answers your question.
http://www.symantec.com/connect/forums/uninstalling-sep-remotely
http://www.symantec.com/connect/forums/remote-uninstallation
https://www-secure.symantec.com/connect/forums/uninstall-client-remotely
Hope that helps!!