How to reset your iPhone to factory settings

I've just had my iPhone replaced by O2 under the insurance I had taken out with them. My iPhone had developed several faults and after a discussion with O2's customer service they agreed to replace it.

Anyway before they took my faulty iPhone away, I wanted to be sure it went back to them without any of my personal data on the device and easily accessible.

Now I know as with any device that stores data on a HDD or SSD, that with the right tools the data can be recovered or accessed, but the following process put my iPhone back to its factory settings.

1. Connect your iPhone to a mains outlet.
2. On your iPhone select SETTINGS - GENERAL - RESET, and you will be presented with the choices below.
3. Select "Erase All Content and Settings" from the options, and you will be presented with the warning "This will delete all media and data, and the reset all settings. This will take about an hour". Just tap the option to "Erase iPhone" as shown below, and then within an hour, you will have an iPhone back to factory settings, all your information erased.