Wiping your iPhone's memory clean may be the only way to fix it. If you have syncing issues, application problems or a lot of freezing on your iPhone, doing a full restore could solve problems. Also, you have the choice of starting from scratch with your iPhone or backing it up to keep your applications and any important information you have stored.
1.Open iTunes on your computer.
2.Connect your iPhone to your computer using the USB cable that came with it.
3.Click the iPhone icon under "Devices" on the left side of the iTunes window. This will open options for your device in the main window.
4.Click the "Summary" tab.
5.Click the "Restore" button
6.Select "Back Up" from the pop-up window that appears. This will back up the information on your iPhone so you can put it back on the phone after it is restored. You can select "Don't Back Up" if you do not want to use this option or you just synced your iPhone to iTunes. If you want to erase everything from the phone after the restore, you must delete the items in iTunes so it does not resync with the phone.
7.Click "Restore" when the window pops up.
8.Click "OK" when the restore finishes. You will get the "Connect to iTunes" message on your phone. Do not disconnect the phone from the computer, and wait until the message disappears or "iPhone is activated" appears on the screen.
9.Select "Set up as new iPhone," or choose a restore point from the screen that appears on iTunes and click "Continue" to complete the restoration.