Reformat your iPhone so that you can either sell or trade it. The factory reset reformats the internal drive on the iPhone, and restores original software and settings. All of your email and storage accounts, files and settings are deleted. If the iPhone becomes unresponsive, reformatting the device will often resolve the issue. Reformat the iPhone through iTunes while the device is connected to your computer, or use the Reset feature in the Settings options to perform the factory reset from within the operating system.
