I have noticed a lot of my clients are still running Windows 8.0. An update was released last October called Windows 8.1. This update is free, easy to start, makes Windows 8 more user friendly, as well as other improvements. Typically updates are downloaded and installed automatically. Oddly, to update to Windows 8.1 users had to manually start the upgrade.
The quickest way to tell if you are running Windows 8.0 is to see if the start button is present or not (see image). If you don’t see the start button, plan on upgrading soon.
PC Magazine also has provided a good upgrade walk through.