Open the App and click on the settings cog (you can see the settings for the App version whether you are logged in to your Formitize account or not).
Under the Settings list, you can see the App's version number.
If you're unsure of whether you have the latest version of the App, then you can go to the Google or Apple App store and search for Formitize. It will let you know there if there is an updated version of the App or not, and you can update it from there.