Apps are continuously updated by the developers. Any app that receives an update will show a notification in the App Store on your iPad. You can update apps at any point by opening the App Store, tapping on Updates and then selecting which app(s) to update.
Apps that are installed via Self Service might need updated from time to time. If you want to ensure you have the latest version of an app you will need to open Self Service and tap the Reinstall button underneath the app. This will update the application to the latest version available.