Use uninstaller software, such as Revo Uninstaller, IObit Uninstaller, Geek Uninstaller. There are more.
These can be used to start the un-installation process of the software. These start the normal un-installer functionality from Windows itself, and when that is done, it will go and check if there are still settings left in the Windows registry and/or files that were no deleted. You can then clean out the remainder and you are good to go to either re-install "fresh" or use the portable version that takes its settings only from the included configuration file.