Although the Windows 8.1 update is downloaded and installed from the Store, your PC needs a Windows Update, KB 2871389, before Windows 8.1 becomes available to you in the Store.

If you’re using Windows Update to get automatic updates, KB 2871389 will be downloaded and installed automatically.

If you’ve turned off automatic updates, if your PC is new and automatic updates haven't been downloaded yet, or if you’d rather not wait for Windows Update to do this automatically, you can go to Windows Update and install KB 2871389 manually.
To install the required Windows Update
1.Open Windows Update by swiping in from the right edge of the screen (or, if you're using a mouse, pointing to the lower-right corner of the screen and moving the mouse pointer up), tapping or clicking Settings, tapping or clicking Change PC settings, and then tapping or clicking Windows Update.
2.Tap or click Check for updates now, and then wait while Windows looks for the latest updates for your PC. If you don't have automatic installation of important updates turned on, you might need to tap or click Turn on recommended settings before you can check for updates.
3.If updates are found, tap or click the message telling you how many updates will be installed automatically. In the list of updates, look for one that includes (KB2871389) in the name (the exact name will vary, depending on your system.).
4.Tap or click Install to install all the recommended updates in the list.
5.When the updates are done, you’ll need to restart your PC. If you have any desktop apps open, save your work and close them before restarting. To restart, swipe in from the right edge of the screen (or, if you're using a mouse, point to the lower-right corner of the screen and move the mouse pointer up), tap or click Settings, tap or click Power, and then tap or click Restart.
6.After you’ve restarted your PC, on the Start screen, tap or click Store, and you should see the Windows 8.1 update. For more detailed info about installing Windows 8.1, see Update to Windows 8.1 from Windows 8.

Some editions of Windows 8 don’t support updating to Windows 8.1 from the Store. These include the following:

• Windows 8 Enterprise. Talk to your system admin about updating to Windows 8.1.
•  Windows 8 Pro, if installed by an organization or a program that uses Volume Licensing. Talk to your system admin, or the administrator of the program that was used to install Windows 8. If you’re the administrator, you can find more info and links to Windows 8.1 ISOs in the Windows 8.1 Enterprise Evaluation.
•  Windows 8 Pro, if installed using an MSDN or TechNet ISO, and activated using Multiple Activation Keys. You might be able to download a Windows 8.1 ISO from MSDN or TechNet.
• Windows 8.1 Preview or Windows RT 8.1 Preview. You might still be able to update from the Store. For more info, see Update from Windows 8.1 Preview to Windows 8.1.
To find out what edition of Windows is on your PC, see Which Windows operating system am I running?

Otherwise, you might be able to perform a clean install of Windows 8.1. For more info, see How to perform a clean installation of Windows.

To refresh the content in the Store
1. Swipe in from the right edge of the screen, and then tap Search.
(If you're using a mouse, point to the upper-right corner of the screen, move the mouse pointer down, and then click Search.)
2.Enter run in the search box, and then tap or click Run.
3.Enter wsreset.exe in the Run command and then tap or click OK.
4.Restart your PC.
5.On the Start screen, tap or click Store, and check to see if Windows 8.1 now appears on the Store home screen.