Microsoft released the final version of its latest operating system Windows 8.1. This will be a Free upgrade if you own a Windows 8. If you open the Windows Store on your PC it will shpow the upgrade available notification.
The Start button is back, Which will take you to the home screen. (you can use the windows key on your keyboard too). Your lock screen displays a slide show of your favorite photos. Plus, you can answer Skype calls, and take photos before you even unlock your PC. The start screen shows live updates.
There are new applications on the Windows store which will only support the windows 8.1 like Facebook official application for windows 8 will only support 8.1
Read more here on what is new
To upgrade to Windows 8.1 you can use this link from windows 8 PC. It will open the link in app store.