These days, I had to upgrade several XP PCs to Windows 8.1, and since I had several W8 upgrade licences in my office, and since the migwiz tool on Windows 8.1 does not accept data from XP, I had to go through Windows 8.
Unfortunately, a fresh installed Windows 8 does not let you install Windows 8.1 upgrade from the store, you have to install first several Windows updates.
Fortunately, I found that the needed updates are only two, both near to the bottom of the update list.
So you can let search fpr updates, deselect all important updates clicking on the top checkbox near to “Name”, scroll down to thhe bottom of the list and select only these two updates. Let complete the update and reboot. Then enter the store and you can install Windows 8.1 from there.
P.S. there is a nice thing: the fresh installed Windows 8.1 has the recently published update to Windows 8.1 already integrated, so you save a lot of updates.