To update the ZTE Z851m you need to install an alternate firmware (ROM). If the device does not automatically update by itselves. You can use the new firmware for your smartphone.
You have to choose the firmware version and follow the instructions. If you have a trouble in update you can write about it in the comments below, we’ll help you.
There are four ways ZTE update:
If you want to install a ZTE update using recovery – download the official update, reboot your phone or tablet into recovery mode and click “Install update from SD card”.