The uninstaller app is included in the installation .dmg image and is only required if you wish to completly remove all components of the IVPN application from your macOS computer. It is not required before installing a new version.
You can download the latest .dmg image from the following link: https://www.ivpn.net/setup/mac-osx.html
Open the downloaded image file and scroll down until you see the "Uninstall IVPN.app".
After running the uninstaller app, restart your macOS computer system.