The OS is for devices running Android 6 only. To update a device from Android 5 to Android 6 you’ll have to send your device to a Handheld Service Center. To do so please Contact Support
An Android 9 OS will always start with NX2V400R001C01, Android 7 OS will always start with NX2V100R001C03 and an Android 6 OS will start with NX2V100R001C02.
You can find the latest updates under Settings > About device > System updates. You can use the downloads at the bottom of this page to install the latest full OS version instead of incremental updates. To install an OS as a ZIP-file, follow the guide here.
See the release notes for this article here.