applications - 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.