Apple frequently issues software updates for your iPhone to make it run faster, safer and more efficiently. For this reason, you should regularly sync your iPhone with iTunes and check for available updates. You need iTunes to download and install these updates on your iPhone. You also need time and some measure of patience; software updates can sometimes take a long time to download due to their size. But, the improved performance, stability, security and added features that you enjoy afterward on your iPhone make updating well worth the effort.
Launch iTunes on your computer. You'll see a navigation sidebar on the left and a main pane on the right.
Click on your Web browser to make sure your computer is connected to the Internet. Your home page should display on your screen.
Connect your iPhone to your computer using the USB cable that came with it. For best results, plug into a USB 2.0 port, which is typically located behind your computer rather than on its keyboard or monitor.
Click on your iPhone's icon, which should now appear under "Devices" in the left sidebar.
Click the "Summary" tab above the main pane on the right. Next, click "Check for Update," under Version, to check Apple's servers for updates. If the dialog box advises you that your iPhone's software is current, stop here; you're all set.
Click "Next" if the dialog box tells you an update is available. ITunes will then present you with the software license agreement.
Click "Agree." ITunes will download the software update onto your computer and then install it on your iPhone.
Unplug your iPhone from your computer when the message at the top of the iTunes window tells you that it's safe to disconnect your device. Click the "Eject" icon to the right of your iPhone in the left sidebar.
If iTunes advises you that a newer version of iTunes is available, update iTunes first before updating your iPhone’s system software.
New software updates, however well meaning, sometimes contain bugs. Wait a few days after a new update is released and browse through reviews by reputable sources before downloading and installing an update on your iPhone.
Don’t disconnect your iPhone while it is updating. This could damage your operating system. You would then need to restore your device and then start the update process again from scratch.
Occasionally, you will not be able to reach Apple’s servers due to high demand. Unplug your iPhone from your computer and try updating again at another time.