Updates to the iOS, the operating system that runs the iPhone, iPod touch, and iPad, bring bug fixes, tweaks, and major new features. When a new version comes out, you'll usually want to install it right away.
Given that the release of new version of the iOS for the iPhone is usually a bit of an event and widely discussed in many places, you’re not likely to be surprised by its release. However, if you’re not sure whether you have the newest iPhone operating system, the process of checking (and installing the update, if one is available) is quick.
Begin by syncing your iPhone or iPod touch with your computer, either by Wi-Fi or USB. To learn how to install an iOS update directly to your device without using iTunes, read this article.
When the syc is complete, look at the top right of the iPhone management screen. You'll what version of the iOS your device is running and, if there's a new version, a message telling you about it. Beneath that is a button labelled Update. Click it.
NOTE: This article covers updating iPhone firmware only by connecting to iTunes. If you're running iOS 5 or higher, you can update wirelessly. Learn how to do so here.