IMPORTANT UPDATE: This process is no longer valid or necessary with the release of Windows 8.1 on October 17, 2013. Beginning with Windows 8.1, Microsoft no longer sells upgrade licensed versions of Windows 8 for download, only full retail versions.
Purchase a download or boxed copy of Windows 8.1 here, or see Where Can I Download Windows 8 or 8.1? for more options. Then see How to Clean Install Windows 8 or 8.1 for a full tutorial on installing it.
Previously Valid Instructions:
I have always recommended a clean install over an upgrade install for every version of Windows, and that's no different with Windows 8. A clean install, or "custom" install, means an installation of Windows 8 from a formatted drive.
As cumbersome as backing up your data beforehand and then restoring it and reinstalling all of your software afterwards may be, your new Windows 8 setup will likely be much more stable than it would have been had you performed an in-place upgrade.
Note: This process is intended to help you get your downloaded Windows 8 or Windows 8 Pro Upgrade prepared so that you can perform a clean install. If you have any sort of retail version (a non-upgrade version) of Windows 8, you can skip on to How To Clean Install Windows 8 for the complete walkthrough.
Important: Even though you're going to completely remove it, your computer must already have Windows on it if you want to install an upgrade licensed copy of Windows 8. See my Installing Windows 8 FAQ for more on this, plus answers to some other questions you might be having right now.
Time Required: This process should take around 30 to 90 minutes, on average, depending on the speed of your Internet connection. This time estimate does not including the actual clean install process, which I link to in the last step.
Click the "Upgrade now" button on the Buy Windows page on Microsoft's site. A file by the name of WindowsUpgradeAssistant.exe will be downloaded. Save it to your Desktop or other familiar location.
Note: This isn't the only way to download Windows 8 but it's certainly the most typical, especially for most home users. See Where Can I Download Windows 8? for more options.
- Run the program you just downloaded from the computer you plan on upgrading to Windows 8 on. If that's a different computer than the one you're on, move the program file there.
Important: This tool provides valuable information about your computer's compatibility with Windows 8, facilitates the purchase of the Windows 8 download, and then downloads the correct version (32-bit or 64-bit) based on information about your current Windows installation - all important reasons to run this tool from the PC you're going to clean install Windows 8 on.
- On the Here's what we found screen, which you'll see after a few minutes, you'll be presented with information about what programs and devices on your computer are, and are not, compatible with Windows 8.
Most things should be compatible but some may say that you need to reinstall it in Windows 8 or visit the provider's website for more information. Since you're doing a clean install and will be installing your software again from scratch anyway, most of that won't matter to you. If you do see an issue, investigate it accordingly.
- Click the Next button once you've read through all of the compatibility details.
- On the Choose what to keep screen, choose Nothing and then click Next.
Choosing any other option (e.g. Windows settings, personal files, and apps or Just personal files), if you get one, would begin some varying degree of upgrading, which you're not doing.
- Click the Order button on the Windows 8 for you screen, next to either Windows 8 or Windows 8 Pro and follow the ordering instructions given.
Tip: There's no need to order the Windows DVD since you'll be downloading a full disc image which gives you the ability to make your own disc for backup.
- Your Windows 8 product key will be displayed on the Thanks for your order screen, which you'll see after your order successfully processes.
Important: Don't lose your product key! You'll need your product key each time you install Windows 8. You should also have received an email with your Windows 8 order and that email also contains a copy of your key. Save it, print it, whatever you need to do. Just don't lose it.
- Next is the Downloading Windows 8 screen. Depending on how fast your connection to the Internet is, and how busy the file hosting servers are, this could take anywhere from several minutes to several hours.
Note: Windows 8 isn't installing right now, the installation files are just being downloaded to your computer in preparation for the next step.
- Once the download is complete, you'll see Checking the download and Getting files ready screens. Just wait those out.
- On the Install Windows 8 screen, choose Install by creating media and then click Next.
If you Install now, you'll be upgrading from your current operating system (e.g. Windows 7, Windows Vista, or Windows XP) but what you want to do is boot from some media, like a disc or a flash drive, so you can perform a clean install of Windows 8.
Important: The Install by creating media option is not available if you're running Windows XP. If you are using Windows XP, follow the above steps from another computer with a more recent version of Windows. Once you have your media created (Steps 11 to 14 below), bring it back to the Windows XP computer and then perform the clean install (Step 15 below). If you're already in this deep, continue without choosing this option and then see this for a solution.
- On the Choose which media to use screen, you can choose either USB flash drive or ISO file.
If your computer does not have an optical drive, or you'd prefer to install Windows 8 via a flash drive, choose USB flash drive, click Next, and follow those instructions. When that's complete, skip to Step 15 below.
If you plan on installing Windows 8 from a disc, choose ISO file, click Save, and continue on to Step 12. An ISO file is a perfect image of a disc, in this case a Windows 8 installation disc.
Tip: If you're not sure what to choose, ISO file is a safe choice because it's relatively easy to create either a disc or a flash drive with the Windows 8 installation files on them if you have an ISO file.
- Assuming you choose ISO file, pick a location to save the ISO file to in the next window, like your Desktop, and then click Save.
- Wait on the Creating the ISO file screen until that's complete.
A Windows.iso file will be created on your Desktop, or wherever you decided to have it saved to in the last step.
- Next you'll see the Burn the ISO file to a DVD screen, plus a reminder about your product key.
You can either click the Open DVD burner link and burn the ISO file to a disc that way, or you can just click Finish and use whatever other disc burning program you'd like. See How To Burn an ISO File to Disc if you don't use the built-in tool.
Clean install Windows 8!
Now that you have the Windows 8 installation files on a flash drive (from Step 11) or on a disc (from Step 14), you can now start the clean install process.
Tip: If you found yourself with an ISO image but you now want that on a flash drive, see How To Install Windows 8 From a USB Device for help.