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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 Backup & reset.
Press Factory data reset.
2. Restore factory default settings
Press RESET PHONE.
Press Delete all.
Press RESET. 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.