If you didn't line up at your local Apple Store or preorder an iPhone 5, you can still upgrade your iPhone, iPad, and iPod Touch to the latest version of iOS released today. I should say it's likely you can upgrade your current device because the new version of Apple's mobile operating system, iOS 6, is compatible with most but not all previous-generation devices. Here's Apple's list:
You have two methods for downloading and installing iOS 6. You can simply update your iOS device over the air via the device's Settings, or you can connect it to your computer and use iTunes.
Method 1: Over the air
The easier of the methods is to grab your iPhone, iPad, or iPod Touch and update wirelessly. Before doing so, however, it's wouldn't be a bad idea to sync your device with iTunes if you haven't done so in a while. There have been instances with past iOS updates where users have reported the new iOS didn't install correctly, bricking their phone and forcing them to restore their phone before trying again. So, if your iOS device has talked to iTunes recently, go ahead and go to Settings > General > Software Update.
You should see iOS 6 listed, with a Download and Install button below it. Tap the button, agree to Apple's terms and conditions, and either heed or ignore Apple's advice to connect your device to a power source during the download to save battery.
After iOS 6 installs, your device will restart, which was a rather lengthy process in my experience (20 minutes or so, after the roughly 45 minutes it took to download and install). After restarting, you'll be greeted by a shiny, new iOS 6 lock screen. Slide to open your device and click through the following four setup screens:
Method 2: Update via iTunes
If you are near your computer with iTunes, it might be faster to update this way. In my experience, updating my iPad 2 via iTunes was faster than updating my iPhone 4S over the air. The first order of business is to update iTunes to version 10.7. Open iTunes and then click iTunes > Check for Updates to install the latest version.
Once iTunes is up-to-date, connect your iOS device. Click on your device under the Devices header in the left-hand column and click Check for Update.
A pop-up window will appear, alerting you that a new iOS version is available for your device. Click the Download and Update button. (Or, if you are going to need your phone in the near future, opt for the Download Only button to download it now and install later. iOS 6 is a 626MB download for the iPhone, which could take an hour or more, depending on your connection and the amount of traffic hitting Apple's servers.)
Click through two more setup screens that show you iOS 6's many new features and Apple's terms and conditions to start the download.
Once the download is complete, keep your iOS device connected until it restarts. After restarting, you will need to hop through four setup screens before you are off and running with iOS 6. On my iPad 2, the process looked like this: