How to Determine the iPhone iOS
Every new model of iPhone released features a new version of the iOS--the operating system that runs the iPhone. It's important to know what version of the iOS is on your phone so you can consult the appropriate user's manual when you are seeking further information about the device. Also, certain apps and hardware are only compatible with certain versions of the iOS. You can find out what version of the iOS is on your phone through either the iPhone's Settings app, or by connecting the device to the computer and opening iTunes.
Tap "Settings" on your home screen. This is the gray icon with an image of gears.
Tap "General" in the Settings screen.
Tap "About" in the General section.
Scroll down the page. The iOS is listed next to "Version."
Connect your iPhone to the computer using the USB cable that came with the device.
Open iTunes if it does not open automatically.
Click the name of your iPhone, listed beneath Devices on the left side of the program window.
Select the "Summary" tab on the right side of the program window. The iOS is listed under Software Version.