You should have received a version upgrade notification which will have the SPS SBE 4.0 M# that you can login to FileConnect with, in order to obtain SEP SBE 12.1. Along with the Version Upgrade will be the license files that you can use to activate the product with.
If you are unable to locate, you can try using the Licensing Portal. Just follow the instructions here:
How to upgrade your SEP11 license to SEP12 online
https://www-secure.symantec.com/connect/articles/how-upgrade-your-sep11-license-sep12-online
Note, if you are not the current registered Licensing Portal owner for SPS 3.0, you may not be able to do the above Version Upgrade process.
If you require further assistance with this, please contact Customer Care at: http://www.symantec.com/business/support/assistance_care.jsp