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If your phone gets slow or doesn't work as it usually does, it may help to restore the factory default settings. All settings and configurations you've made on your phone are deleted.
1. Find "Factory data reset"
Press Additional Settings.
Press Back up and reset.
Press Factory data reset.
2. Restore factory default settings
Press Erase All Content and Settings.
Press Delete Data.
Press Delete Data. Wait a moment while the factory default settings are restored. Follow the instructions on the screen to set up your phone and prepare it for use.