There is currently a known Apple bug where your Mobile 4.0 app will not update automatically nor display the "Update" option, even when you have auto-update turned on.
To force the App Store to refresh and display the "Update" option, take the following steps:
1. On your iOS device, navigate to Settings > iTunes & App Store
2. Toggle "Updates" off and on
3. Open the App Store, search for "NuORDER 4.0," and you should see the "Update" option available now.
We recommend always updating to the latest version since we are releasing important bug fixes and performance improvements during our public beta period.