The best way is to allow automatic updates on your mobile device. That way, if there's been an update, you should get a pop-up message when you log in, and all you need to do is follow the instructions to download.
How to allow automatic updates will vary depending on your device – for more information, check its user manual or look up the instructions on the manufacturer's website.
You can also check the Google Play Store for Android or the App Store for iOS to see when a new version becomes available.
Keeping everything updated
Remember that you also need to keep your other separate players up to date as well – namely BBC iPlayer, ITV Hub, All 4, My5 and UKTV Play.
You'll probably be prompted to update them automatically too, but it's worth checking the instructions on each individual player.