HT4623: Update your iPhone, iPad, or iPod touchLearn about Update your iPhone, iPad, or iPod touch
Currently Being ModeratedFeb 11, 2013 4:00 PM (in response to rachael327)
You can't update over the air, because it requires IOS 5.0 or higher.
In order for you to update, you will need to do it in itunes.
Open itunes, then connect your phone to your computer, itunes should automatically pick up that your phone needs to be updated.
P.S. Make sure you backup your phone prior to updating your IOS.