FYI These forums are for the home user oriented Norton product line.For additional information, see Supported upgrade paths to Symantec Endpoint Protection and Symantec Endpoint Protection Migration Considerations.In sepm 12 it was easy (https://support.symantec.com/en_US/article.
A previous version of Symantec Endpoint Protection (SEP) 12.x or 11 exists on the network or on individual computers.
You need to migrate to one of the following versions of Symantec Endpoint Protection 12.1.
The over install process saves the client settings, and then upgrades the client to the latest version.
Note: Clients that are Group Update Providers (GUPs) should be upgraded before other Endpoint Protection clients.
My organization has a large deployment of Symantec Endpoint Protection (SEP) (~20k clients) with a single SEPM instance running in an ESX VM.
We do have many remote clients designated as Group Update Providers (GUPs) where possible.
After you upgrade, the management server automatically starts the service.
You do not need to uninstall previous clients before you install the new version.
This document explains how to update Symantec Endpoint Protection definitions by running Live Update.