From the current release notes
Upgrading to ClearPass Policy Manager 6.2
You can upgrade to ClearPass Policy Manager 6.2 from ClearPass Policy Manager 5.2.0 (non-VM), 6.0.x, or 6.1.x.
Upgrade images for upgrading from 6.0.x and 6.1.x are available on the Software Updates Portal at Administration > Agents and Software Updates > Software Updates.
For appliance upgrades from 5.2.0, the upgrade image is available on the Support site.
Direct upgrades from versions prior to CPPM 5.2.0 are not supported. Customers with earlier versions of 5.x must upgrade to either ClearPass Policy Manager 5.2.0 or 6.x first before upgrading to 6.2.
Direct upgrades from CPPM 5.2.0 VM are not supported. Customers must install the 6.2.x VM version and then migrate their data to this new version.
http://support.arubanetworks.com/DOCUMENTATION/tabid/77/DMXModule/512/Command/Core_Download/Default.aspx?EntryId=11988