Upgrading from 12.5 on Windows 2003 to 2010 R3 on Windows 2008 R2

hi there, i'm in the process of upgrading symantec backup exec for a customer from v12.5 installed on Windows 2003 R2 to v2010 R3 on Windows 2008 R2. I have done this for previous versions but it was all on the same operating system from 9 to 10, 10 to 11, 11 to 12, etc.  I'd like to know how I should proceed with this.  I already have the Windows 2008 R2 server built with the base backup exec 2010 R3 installed, but haven't moved or copied any data.

thanks!