The app version you currently have downloaded can be found in the app itself. You are not required to log in to view this information.
When opening up the app, click the top left-hand corner main menu, and select About. The version will be listed below.
To tell if you are running the most up to date version, head over to the Apple App store or Google Play store and search for HEADCHECK. The latest version will be listed here; if they match, you are good to go! If your version is out of date, please update to the newest version of the app.