Upgrade backup appliance 3600 R2 to R4

Hello,

I have received a notification from symantec that the upgrade for the backup exec appliance R2 and R3 to the new R4 is now available... anyone knows of any documentation or steps or notes about the how to perform the upgrade? the appliance currently uses windows server 2008 R2 and backup exec 2012. what will be upgraded exactly? the backup exec. version or both the OS and the backup exec.?

appreciate any input on this.