First, go to the Windows Store. You'll get to it by clicking on the "Store" icon on the home screen of your computer.
Once in the store, you'll see big prominently that says "Upgrade to Windows 8.1 for free." Click on it.
You will enter the page of Windows 8.1, a screen with more information about the update. Below the title is a button that says "Download". Click on it and begin downloading Windows 8.1.
The download is quite heavy (3.6 GB), so it may take a while. Make sure you have plugged in and that you are using to connect to the Internet faster you have computer access.
When the download is complete, start the installation automatically. A message on the top right of the screen that says "Installing Windows 8.1" appears.
After a few minutes, the system will ask your permission to restart the PC, a necessary step to complete the upgrade. Click on the "Restart Now".
The computer restarts and Windows 8.1, and you just have to research and find update all their news.