Is there a way to revert back to the old version of an iOS app after having it upgraded? I like the older version of the app than the new version and as a friend of mine is still using the old version, I think it mustn't be an absolute requirement from the app developers' end.
Yes, but only if you prepare for the downgrade before updating or catch it quickly after updating.
Now you have a copy of the current version.
Unless you have a backup of your iTunes library, there isn't an official way to obtain old versions of ipa files.