There are two ways Google Nexus firmware update:
If you want to update your phone using recovery – download official update, reboot your phone into recovery mode and click “Install update from SDcard”.
On the greater part of Android tablets and phones, you can lock bootloader and then unlock it using the command line.
These are the things you need to know how to lock bootloader:
Make sure that all of your important files and data are saved!
Having prepared the above, you can start the process of how to lock bootloader:
Done! Now you know how to lock the bootloader using the command line!