As soon as your app closes that screen disappears. So the way to prevent that screen from appears is to close your app as quickly as possible.
If the screen doesn't close by itself then that means your app is still running.
If you're using the AutomaticUpdater then make sure the cleanup happens before InstallNow() is called. If you're using wyUpdate in "standalone" mode, then make sure you cleanup everything (to prepare for a quick exit) before you run wyUpdate.