Here is the step that i took to upgrade DPM 2010 to DPM 2012 in my lab environment.
Before we start make sure that you have perform a DPM database backup.You can backup the database using below method:
a) Backup DPM DB to Tape or
b) Backup DPM DB to DR DPM Server or
c) Lastly, manual backup by execute command
Just open DPM Management Shell, to execute the above command. The database will backup to the following folder:- %program files%\Microsoft Data Protection manager\DPM\Volumes\ShadowCopy\Database Backups
d) Then on the DPM 2010, patch the server with the hotfix KB2615782 from http://support.microsoft.com/kb/2615782 . Once apply the hotfix, upgrade the dpm protection agent.
e) After an agent upgrade is complete, put DPM 2012 CD Media and perform in-place upgrade. Installation is straight forward and hassle free.
f) Lastly, upgrade the entire dpm protection agent to complete the DPM 2012 upgrade.