From ISE Design Suite 12.1 onwards there are no longer any Xilinx entries in the Windows Registry. All the information that was in the Windows Registry is now included in the installation. As a side effect of the Xilinx tools no longer using the Windows Registry, it is no longer possible to use the Windows "Add or Remove Programs" utility to uninstall the ISE Design Suite tools.
Instead, you can uninstall the tools by going to the WindowsStart menuand running the Uninstall process located in the Accessories folder within the Xilinx ISE Design Suite 12.x Start Menu program folder.
Alternatively, you can run "xsetup -uninstall" using the xsetup executable found in the common folder. This is also the method to uninstall on Linux.