Hello,
The AutoUpgrade process lets you automatically upgrade the Symantec Endpoint Protection client software for all the clients that are contained in a group. For example, you can use AutoUpgrade to upgrade clients to a new maintenance release or product version.
You must test the AutoUpgrade process before you attempt to upgrade a large number of clients in your production network. If you do not have a test network, you can create a test group within your production network. For this kind of test, you add a few non-critical clients to the test group and then upgrade them by using AutoUpgrade. You confirm that the upgrade completed successfully by verifying the version number of the client software. The version number is displayed in the client's Help >About panel.
When creating a custom packages for the Auto-Upgrade, you may like to check this below article:
Creating custom client installation packages in the Symantec Endpoint Protection Manager console version 12.1
http://www.symantec.com/docs/TECH165801
https://www-secure.symantec.com/connect/articles/how-do-i-create-and-configure-custom-symantec-endpoint-protection-installation-package-vers
How to export Symantec Endpoint Protection (SEP) client install packages without any definitions or package with Basic Content.
http://www.symantec.com/docs/TECH178698
Upgrade clients to SEP 12.1 by Auto upgrade feature
https://www-secure.symantec.com/connect/articles/upgrade-clients-sep-121-auto-upgrade-feature
Hope that helps!!
Regards,