Resetting your phone will return it to the same state it was in the first time you turned it on. All of your personal content, including text messages and apps you've downloaded, will be erased, and the phone will be restored to its factory settings.
If you decide to reset your phone, you can backup apps, text messages, photos and more to your Microsoft account in the cloud beforehand.
Be careful. Resetting your phone will erase all content stored on your phone, including apps, text messages, call history, music, photos and more.
To reset your phone
1. In the App list, tap Settings.
2. Tap About, then tap Reset your phone.
3. You'll receive two warnings. If you're absolutely sure you want to restore your phone to its factory settings, tap Yes, then tap Yes again.
It might take a little while for the process to complete.