You will most likely need to reinstall the version you are trying to uninstall with the parameter /ForceInstall . If you don’t have the installer anymore, you can download most versions here:
If you are using an older version you may have a look here:
This should create the proper unins000.dat again and allow you to uninstall the application.
To execute an installation with the parameter /ForceInstall you can create a Windows shortcut of the file and add the parameter /ForceInstall to “target” in the shortcuts properties. Afterwards please restart your computer, then the update should work.