Why does everything have to be updated via download? That's completely fucked up! In the good old days you could download an ISO-image and update when you wanted and as many things you needed. The same plague is in Mac OS X, Windows, all important applications. I hate this!
Next thing I do is take my trustworthy Windows 7 USB/DVD download tool to create a bootable USB-stick from the 8.1 upgrade ISO-file. A boot from the stick and got into installer which said that this is not the way to do the upgrade. Come on! Second boot back to Windows 8 and start the upgrade from the USB-stick said that "Setup has failed to validate the product key". I googled that and found a second article about getting the ISO-file (Windows 8.1 Tip: Download a Windows 8.1 ISO with a Windows 8 Product Key), which had a comment from Mr. Robin Tick had a solution for this. Create the sources\ei.cfg-file into the USB-stick with contents:
[EditionID] Professional [Channel] Retail [VL] 0
Then the upgrade started to roll my way. To my amazement my BitLocker didn't make much of a stopper for the upgrade to proceed. It didn't much ask for the PIN-code or anything, but went trough all the upgrade stages: Installing, Detecting devices, Applying PC settings, Setting up a few more things, Getting ready and it was ready to go. It was refreshing to experience success after the initial failure. I'm guessing that the BitLocked made the downloaded upgrade to fail.
Next thing I tried was to upgrade my office PC. It is a Dell OptiPlex with OEM Windows 8. Goddamn it! It did the upgrade, but at that point my OEM Windows 8 was converted into a retail Windows 8.1. Was that really necessary? How much of an effort would that be to simply upgrade the operating system? Or at least give me a warning, that in order to proceed with the upgrade the OEM status will be lost. Come on Microsoft!
You can change it if your product key is for some other edition. The original article said Professional and since my product key is for Windows 8 Professional, that's why I have that in the ei.cfg. I urge you to put the correct edition into the ei.cfg-file, unless you don't want to do a complete re-install.