If you're being asked to update your TVNZ+ app, it will be because our engineers have made an update that's critical to its use. Keeping your TVNZ+ app updated regularly will ensure that you have all the latest and greatest feature and performance improvements.
Take a look at the following articles to get more specific details on how to do this for your device.
Apple TV - How do I update TVNZ+ app on Apple TV?
Android TV - How do I update the TVNZ+ app on Android TV?