Downgrading an iOS application - how to download a previous version?
If you are updating from devices directly, you can only pull the most recent version of the app.  In a slight change from the past, if the most recent version is not compatible with your device, it will now offer to let you download the most recent compatible version instead.

If you use iTunes on a Mac to download copies of your apps into your library, or you sync your iPad with iTunes to do this, then you should have the old version in your library, although if iTunes has also downloaded the new version you may have to hunt in  your time machine backups to find the relevant .IPA file for the older version you need.