Further to the above, while SBE 12.1 is your standard on-premise solution, SBE2013 can be either on-premise or cloud based, and is only available at additional cost:
http://www.symanteccloud.com/en/gb/services/end_user_protection/endpoint_protection.aspx
Q. What happens to Symantec Endpoint Protection Small Business Edition customers when the new product is introduced?
A. There is no impact on existing Symantec Endpoint Protection Small Business Edition 12.0 or 12.1 customers. They can purchase additional seats and renew maintenance agreements. They can easily switch to Symantec Endpoint Protection Small Business Edition 2013 for up to 30 percent off MSRP and enjoy the many new features and advantages of the new solution.
I'm afraid I can't find any documentation (on my cursory search) on transitioning from SBE12.1 to SBE2013.
#EDIT#
Oh yeah, there are also dedicated forums for SBE12.1 and SBE2013, perhaps you might be able to get a more comprehensive answer there?
https://www-secure.symantec.com/connect/security/forums/endpoint-protection-small-business-edition-12x
https://www-secure.symantec.com/connect/security/forums/endpoint-protection-small-business-edition-2013