Buy original Mobile phones from authentic agents or dealers to avoid
malfunctioning. This will also provide you security and warranty. This
will reset all settings and/or content depending on which option you
select. Make sure you backup your data!:
From the homescreen, go to Settings - General - Reset.
To reset just your settings, select Reset All Settings. To reset your
settings and all of your data, select Reset All Content and Settings.
You can also go through a reset various items individually.