How to downgrade an app if it has been updated via Play Store? I have an app installed on my phone, which I've installed from the Google Play Store.  If I update the app and don't like the upgraded version, is there a way to undo the update and downgrade back to the version of the app that I had previously installed?

I tried searching a bunch on this site, and I found lots of questions about downgrading the OS/ROM/firmware, but nothing about downgrading app versions or reverting an app update.
There is an idea  by Firelord in the comment here which I think should work: 


  The best way I think is to have a backup of the app (at least its APK if not the data files; APK of earlier version of an app can also be obtained from some websites (beware of malware) if you updated the app and doesn't have the backup) so that if you end up disliking the updated version, then you can simply use that APK to revert back to previous version. That was for non-rooted devices. For a rooted device, well, use Titanium Backup to take complete app backup.