Completely Uninstall ArcGIS for Desktop
Uninstalling ArcGIS for Desktop, completely uninstalling it, requires more than simply uninstalling the program using the Windows uninstall dialog. To completely expunge ArcGIS for Desktop from your system requires uninstalling the software, deleting directories in your user profile and removing hives from the registry. If you are not familiar or comfortable making these types of changes to your computer, please do not dig into these parts of your machine and find somebody who is.
1 - Uninstall
If you are still with me, let's get started. The first step is pretty boilerplate. Uninstall the software by going to Start > Control Panel > Programs and Features. From this dialog, select ArcGIS 10.1 for Desktop and uninstall it. Once you start this, go do something else for about a half hour to an hour. This will take some time. Once ArcGIS for Desktop is uninstalled, if you have Desktop Background Geoprocessing installed, uninstall this as well.[gallery link="file" ids="1230,1231"]
2 - Remove ArcGIS Directories
Open up Windows Explorer. The quickest way is to press the Win and E keys simultaneously. You are going to need to remove directories from three places. If they are already gone do not worry about it. You are just checking to be through. These locations are:- C:\Users\<userLogin>\AppData\Roaming\ESRI
- C:\Program Files(x86)\ArcGIS
- C:\Program Files (x86)\Common Files\ArcGIS
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3 - Remove ArcGIS Hives from Registry
Last, you are going to have to delete the registry hives related to ArcGIS. This is the step where, if you are not careful, you can break your computer. If you are not comfortable with doing this, find somebody who is. That is my disclaimer.If you still want to get into the registry, hit Win and R to open the run dialog. Type in regedit to open the registry editor. You are looking for two different hives. In the registry editor, a hive looks like a folder. The hives you are looking for are both named ESRI. One is in HKEY_CURRENT_USER/Software/ESRI. The other is HKEY_LOCAL_MACHINE/SOFTWARE/ESRI. The first is gauranteed to be there. The second may or may not be there, depending on your version. Either way, delete them both.
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Congratulations, you have completely removed ArcGIS for Desktop. You have uninstalled, deleted directories and removed hives. Now, you are ready to install a new version. If like me when writing this tutorial, you just removed all traces of 10.1 from your system to get ready for a fresh install of 10.2. Have fun!