Now that you have the KB2871389 update, it's probably time to uninstall and re-install it. The steps below have worked for quite a few people when nothing else worked. It's certainly worth a shot.  1) Uninstall KB2871389 and reboot.  2) Download the KB2871389 update from Microsoft --> [URL] 3) Install the KB2871389 update manually and reboot. 4) You should now (hopefully) see the 8.1 upgrade in the Windows Store.
Hello - I am unable to update from Windows 8 to 8.1; the 8.1 update does not show in the Windows store. I have downloaded all updates for Windows 8 (including KB2871389); I have sync'd my licenses in the store, reset the contents of the Windows store (wsreset.exe), tried going directly to ms-windows-store:WindowsUpgrade and of course restarted after all of these changes.  I am not running a Volume or Enterprise version of Windows 8; I am running plain old Windows 8 - 64bit. What am I missing - please advise. 
Unable to update from Windows 8 to 8.1 Inspiron 5537