Why? This method does not require you to have an active Microsoft LIVE account associated with your Windows 8.x install for access to the Win 8.1 update through the Windows Store. Otherwise, it's the same as the Windows Store Win 8.1 update for all intents and purposes. Keep in mind that downloading the Win 8.1 ISO for this install can be significantly faster than downloading Win 8.1 update through the Windows Store. (Using the fast Internet at the Microsoft store is recommended! Also, some Microsoft Stores have a pre-built image they can provide to you so all you have to do is put/install that on your computer and enter your legal key(s).) Method works under VMWare Player 6 as well, so it's a great way to update your virtual development OS system and keep playing with Win 8.x while running Win 7.x. RAR/ZIP up the final Virtual OS install for safe keeping and fast restores as well. Realistically, expect to spend about 1-2 hours doing steps 1-10. 0. Run a FULL Windows Backup now to an external drive. (optional, but recommended) (Yes, Win 8.1 upgrade is pretty safe and won't nuke most systems, but you never know...) However, if you have only installed Windows Store apps and have all of your files sync'd with Skydrive, feel free to skip this step since everything's on the cloud and will auto-download once you log into your new Win 8.1 install. 1. We'll assume you have a legal Windows 8.x Pro install using a Dreamspark or Retail key. (haven't tested with VL, etc keys) You do not need to have an active Microsoft LIVE account associated with this (can be totally offline until the final key verification process). You can have a legal Media Center key as well (optional) associated with your Win 8.x install. 2. You can download whatever version and 32/64-bit ISO version appropriate for your version of Windows now. eg. Download en_windows_8_1_x64_dvd_2707217.iso (3.63GB) for the Windows 8.1 Pro install ISO. 3. Burn ISO to DVD, Mount ISO as a virtual CD image, create a USB install from the ISO image - do whatever you need to make the contents visible to your Windows 8.x install. 4. Run setup.exe from the ISO to start the Windows 8.1 install process. 5. You can choose to keep apps & files, files only, or nothing. 6. Enter a generic install key (eg. ending with -c9wkb for the pro update). This is not a VALID key but instead, only used to get Win8.1 to install. You will NEED to enter a VALID 8.x key after install to activate Win 8.1. You will NEED to enter a VALID 8.x Media Center feature key to activate that feature. ( IF you disconnect from the INTERNET before entering and clicking NEXT for this generic key, this process can go faster - validating the key internally. Seems when I test it with an Internet connection, this validation process takes longer - not sure why. ) 7. Allow the Win 8.1 update to finish - about 1/2 hour for an i5 CPU. 8. VALIDATE Windows using your LEGAL KEYS. Once you have booted into your new Win 8.1 install, you can now change the Windows key to your valid 8.x key and add the (optional) Media Center feature key back in. TO add your legal Win 8.x key, go to the default Start screen and type "Slui.exe 0x3". Start this program and enter your WINDOWS 8.x key. You will need to be online for this to validate. TO add your MEDIA CENTER feature key, go to the default Start screen and type "Add Features". Start this program and enter your MEDIA CENTER feature key. You will need to be online for this to validate. Once it validates, it'll install the Media Center features and go through a reboot. (DON'T be dumb like me and try many times to enter this Feature Key into the Windows Product Key box above! WRONG WAY TO DO THIS & WON'T WORK!!!) 9. Activate Windows. Type SYSTEM and bring up the SYSTEM control panel. At the bottom of this informational window, it'll tell you if Windows is Activated or not. If not, make sure you're connected to the Internet and click to activate Windows. Shouldn't take more than a few seconds. You may need to close and reopen SYSTEM for this information to update. You may need to click Activate a few times for it to work. 10. Clean up all the INSTALLER files and old OS files left behind after the install. Type "administrative tools" and bring up this window. Select "Disk Cleanup". Click the "Clean up SYSTEM FILES" button. Wait for it to think and process. It'll bring you back to the original window - scroll down and check "Previous Windows installation(s)" along with anything else you don't need. Click OK and it'll delete about 8+GB of useless, old OS files. 11. Run a FULL backup of Windows (optional) Not necessary, but do you really want to spend all this time reinstalling everything again? Best time is now to backup Windows to an external hard drive for peace of mind and a rapid restore in case anything goes wrong later.