iPad and iPhone users running iOS 5 and above now have the ability to install system updates if connected via Wi-Fi. If you are not currently on iOS 5, consult this image on how to update your iPad or iPhone to the latest and greatest iOS version. If you are unsure on how to find your iOS version, view the images above of the Settings screens, or read this post that explains two different methods to find the iOS version currently on your iPad or iPhone.
If you already have updated your device to iOS 5, and see the the purple coloured Software Update notification whilst using a WiFi connection, simply tap the Details button. The Details window actually enables the upgrade if the Install Now button is tapped. This button appears below the descriptive list of fixes and changes contained in the upgrade.
If you opt to install, a Terms and Conditions dialog appears – riddled with indecipherable legalese – tap the Agree button to continue the installation. Next, your iPad or iPhone will validate your device with Apple, download the upgrade package, and reboot.
Finally, the install progress bar screen is displayed, and when done your device will open the Home screen as normal. You may then opt to check the version number using the Settings app mentioned earlier.