first,we need let the Iphone go to Recovery Mode
power off your Iphone,hold the Home Key +Connect USB cable
Then IOS 7 Show you this :
http://www.gsm112.net/Pics/IOS700.png
and if is IOS8 will Show you this
http://www.gsm112.net/Pics/IOS800.jpg
BR,
Saigonmobile