Use this utility to locate and automatically uninstall ArcGIS software previous to version 10.1 (see list below for targeted products).
You must uninstall all ArcGIS products previous to version 10.1 and any third-party extensions or tools from your machine before proceeding with the ArcGIS 10.3 installation. You must also uninstall your ArcGIS License Manager and install the latest 10.3 version. (The License Manager for 10.3 can manage licenses for ArcGIS 10.x and 9.x installations.)
The ArcGIS 10.3 setup package is designed to detect and upgrade existing installations of ArcGIS 10.2.2, ArcGIS 10.2.1, ArcGIS 10.2 and ArcGIS 10.1 (including SP1) on the target system. The settings for the installation location, license manager (for concurrent use), and authorization information (for single use) are retained in the upgrade. The installation location parent folder is retained. If you wish to change the installation location when upgrading from ArcGIS 10.1, 10.2, 10.2.1, or 10.2.2, you will need to manually uninstall that product through Add/Remove Programs in the Windows Control Panel before installing ArcGIS 10.3 in the new location.
While you may be signed in to multiple portals, you can only have one active portal.