76Update and reset
Performing a factory reset (hard reset)
If you’re passing your phone on to someone else or your phone has a persistent problem that cannot be solved, you can do a factory reset (also called a hard reset). This returns your phone to the state it was in before the first time you turned it on.
Factory reset is not a step to be taken lightly. It will permanently delete all your data and customized settings, and will also remove any apps you’ve downloaded and installed. Be sure to back up any data and files you want to keep before you do a factory reset.
Performing a factory reset via settings
The most convenient way to do a factory reset is via the phone settings.
1.On the Start screen, tap 
.
2.Tap Settings > about phone.
3.Tap reset your phone, and then tap yes.
Performing a factory reset using phone buttons
If you cannot turn on your phone or access the phone settings, you can still perform a factory reset by using the buttons on the phone.
1.With the phone turned off, press and hold the VOLUME UP and DOWN buttons, and then briefly press the POWER button.
2.Wait for the screen to show the instructions on how to do the factory reset, and then release the VOLUME UP and DOWN buttons.
3.Follow the instructions onscreen to factory reset your phone.