Restoring the iPhone using iTunes will result in the loss of all data stored on the device including 3rd party applications.
This type of reset should only be used as a last resort after all other troubleshooting steps have been exhausted. It is highly recommended that you complete a backup of the device information before proceeding with the steps in this tutorial.
The computer will need to have the latest version of iTunes installed. iTunes can be downloaded from the Apple website: http://www.apple.com/iTunes
Connect the iPhone to the computer using the supplied USB cable.
Open the iTunes application on the computer, then click iPhone.
Note: If the sidebar is displayed, click the iPhone name under DEVICES.
Click Restore iPhone.
Read the iTunes alert message and click Restore.
Click the Next button in the iPhone Software Update window.
Read the software license agreement, then click Agree.
iTunes will begin restoring the iPhone to its default settings. Do not disconnect the iPhone from the computer.
Once the restore is complete and the iPhone restarts, iTunes will display the Welcome to Your New iPhone screen.
Select the desired option and click Continue.
Click the Get Started button.
Click the Name field and enter a name for the iPhone, then click Done.
The iPhone is now setup and ready to use.