Common supported upgrade paths are as follows:

• Symantec Endpoint Protection 11.x (enterprise version) to Symantec Endpoint Protection 12.1.x (enterprise version)
  See: Supported upgrade paths to Symantec Endpoint Protection Manager 12.1 from Symantec Endpoint Protection Manager 11.x
   
• Symantec Endpoint Protection 12.1.x to Symantec Endpoint Protection 12.1.x (the latest Release Update)
  Applies to Small Busines Edition and enterprise version. Upgrading to the latest Release Update of 12.1 is always recommended.
  See: Supported upgrade paths to Symantec Endpoint Protection 12.1.2
   
• Legacy security product to Symantec Endpoint Protection 12.1.x
  See: Migrating from Symantec AntiVirus or Symantec Client Security to Symantec Endpoint Protection 12.1 or later
   
  Note: Migration from Symantec Sygate Enterprise Protection (SSEP) 5.1, Symantec AntiVirus 9.x and Symantec Client Security 2.x are not supported as of Symantec Endpoint Protection 12.1.2.
  All versions of Symantec Sygate Enterprise Protection up to 5.1 (5.1.1) can be migrated to version 12.1, 12.1.1000 or 12.1.1101. Releases later than 5.1 cannot be migrated.
   
• Symantec Endpoint Protection 12.0 Small Business Edition to Symantec Endpoint Protection 12.1.x Small Business Edition
  This is considered a cross-grade.
   
• Symantec Endpoint Protection 12.0 Small Business Edition to Symantec Endpoint Protection 12.1.x (enterprise version)
  This is considered an upgrade.
   

Unsupported paths:

• Symantec Endpoint Protection 11.x or 12.1.x (enterprise version) to Symantec Endpoint Protection Small Business Edition
  This is considered a downgrade, and it is not supported.
   
• Symantec Endpoint Protection 11 Release Update 7 or later to Symantec Endpoint Protection 12.1 RTM (12.1.671)
  The database schema are incompatible.
   
• Symantec Endpoint Protection Release Update 7 Maintenance Patch 1 (11.0.7101) or Release Update 7 Maintenance Patch 2 (11.0.7200) to Symantec Endpoint Protection 12.1 (12.1.671) or 12.1 Release Update 1 Maintenance Patch 1 (12.1.1101)

 Be sure to consult the Release Notes for the version to which you are about to upgrade.

 
License Update actions during upgrade:

• Symantec Endpoint Protection 11.x (enterprise version) to Symantec Endpoint Protection 12.1.x (enterprise version)
  Adds and activates upgrade license.
   
• Symantec Endpoint Protection 12.0 Small Business Edition to Symantec Endpoint Protection 12.1.x Small Business Edition
  Keeps the same license.
   
• Symantec Endpoint Protection 12.1.x Small Business Edition to Symantec Endpoint Protection 12.1.x (enterprise version)
  Removes old licenses, adds and activates upgrade license.
   

Technical Information

• MR = Maintenance Release (Symantec Endpoint Protection 11.x, versions prior to 11.0.5002)
• RU = Release Update (Symantec Endpoint Protection 11.x, 11.0.5002 and later)
• MP = Maintenance Patch (applies to MR or RU)
• PP = Point Patch (applies to MP; not very common)