Windows 8.1 update cannot be found in the Windows Store

Symptom:
If your computer is running Windows 8 (or Windows RT) and you want to update to Windows 8.1 (or Windows RT 8.1), in most cases you will see this free in the prominent location on the Windows Store home page. Update.
Cause analysis:
There are several reasons why you can't see the Windows 8.1 update in the Windows Store. Please check the details to determine the solution.
Solution:
There are several reasons why you can't see the Windows 8.1 update in the Windows Store. Please check the details to determine the solution.
1. Confirm that the user is not using Volume Licensing, Windows 8 Enterprise or Windows 8/8.1 Preview.
2. Confirm that the user has installed KB2871389. If there are other updates that have not been installed, confirm that the user has completed the installation. Upgrading to Windows 8.1 requires the Windows Update service.
If there are other updates in the queued installation, the Windows 8.1 update will not be available.
3. Run WSreset.exe from the command line, which will clear the app store cache.