Resetting your iPhone takes it back to the way it was when it came out of the box. This can be handy if you’ve installed a bunch of apps and your home screen is a mess, or if you’ve misspelled words and the misspelling have been incorporated into your dictionary. To reset the device, simply tap on Settings in your Home screen and then navigate to General >Reset.
From this screen at right you can reset or restore your content and settings, network settings, keyboard dictionary, home screen layout or location warnings. Be warned these resets can’t be undone. Note that if you have set a passcode on your device, you have to enter it before you can reset the device.
Resetting a locked up iPhone
Holding down the power button on top of the iPhone will give the option to power off the phone. But what do you do if your phone locks up and does not respond when you press that button? Try holding down the power button and the Home button at the same time. Keep holding them until the phone resets or shuts off, then let go.