If you are selling your iPhone or exchanging it for an upgrade, you can delete all of its data with the iTunes application. Making sure you remove all of your information from the phone is important for keeping your messages, addresses and applications secure from unknown users. Before deleting all of your data, make sure you back up any information you still need and use.
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Connect your iPhone to the computer by inserting one end of its USB cable into the iPhone's data port and the other end into the computer's USB port. Wait for iTunes to launch. If iTunes does not open on its own, double-click its icon to open the program.
Click on the iPhone icon beneath "Devices" on the left side of the iTunes screen.
Click "Settings" and click "General."
Click "Reset" and "Erase All Content and Settings." Click "Yes" when asked to confirm your decision. Wait for the completion message before disconnecting your iPhone from the computer.