In the registry tree (in the left pane of the registry window), go to 'My ComputerHKEY_CURRENT_USERSoftwareESRI', and click the registry key, 'Desktop 10.x'. For Pro click the registry key 'Pro1.0'. (For version 9.3.1 and earlier versions, go to 'My ComputerHKEY_CURRENT_USERSoftware', and click the registry key ESRI.)