Resetting your Windows phone will return it to the same state it was in the first time you turned it on. All of your personal content will be erased, and the phone will be restored to its factory settings.
If you decide to reset your phone, you can back up apps, text messages, and more in the cloud beforehand. To learn more about how this works, see Back up your stuff.
Warning: Be careful. Resetting your phone will erase all content stored on your phone, including apps and games (along with app data and game progress), text messages, call history, music, photos, and more.
Reset your phone
On Start , swipe over to the All apps list, then select Settings .
Select System > About > Reset your phone.
You'll receive two warnings. If you're absolutely sure you want to restore your phone to its factory settings, select Yes, and then select Yes again. It might take a little while for the process to complete.
If your phone is unresponsive and you can't reach Settings , you may be able to reset your phone using the hardware buttons. On Lumia phones (and some others), use the following procedure to reset your phone.
Reset an unresponsive phone
Press and hold the Volume down and Power buttons at the same time until you feel a vibration (about 10 to 15 seconds).
When you feel the vibration, release the buttons, and then immediately press and hold the Volume down button until you see a large exclamation mark.
Once the exclamation mark appears, press the following four buttons in this order: Volume up, Volume down, Power, Volume down. Your phone should now reset and restart itself. (It might take a while for the reset to finish.)
Note: If you lose your phone, you can reset it remotely. To learn how, see Find a lost phone.