With September 2011's Windows 8 Developer Preview, only clean installs of the OS were supported. But with the advent of the Windows 8 Consumer Preview, eager enthusiasts can now choose an in-place upgrade install as well.
Note: This guide will examine the in-place process that utilizes the traditional, media-based upgrade method. Windows 8 features a new web-based installer that has proven to be a quicker, easier, and more reliable method of upgrading, so I'll be focusing on that method in Windows 8 Secrets.
A couple of other notes before we get started.
You are only able perform a true in-place upgrade from Windows 7 to the Windows 8 Consumer Preview and, yes, the migration is irreversible, a one-way process that can't be rewound. So upgrading from Windows Vista is not supported, nor is upgrading from the Windows 8 Developer Preview: Microsoft tells me it has blocked that from working. But understand what that means: Only with Windows 7 can you literally upgrade in-place; with the other OSes,you can only bring over some subset of personal files and settings to the new install.
This guide will only examine upgrading from Windows 7, which is by far the most common upgrade scenario.
Also, it will not be possible to upgrade from the Consumer Preview to the RTM, or final, version of Windows 8. So don't perform this upgrade expecting to be able to do so. As always, it's assumed that only those who know what they're doing will upgrade to a beta version of an OS, even one that is as refined as the Windows 8 Consumer Preview.
As with the clean install process I described in Clean Install Windows 8, this guide assumes you have created Upgrade media in the form of a Setup DVD or USB memory key. (For the Consumer Preview, this is the same ISO used for the clean install process.)
And don't be surprised to discover that the steps described here are very similar to a clean install. It is the same Setup routine, after all. The big difference, from a user experience standpoint, is that an in-place upgrade takes a lot longer than a clean install, and that, unlike previous Windows versions, you can transfer your local account to a Microsoft ID as part of Setup.
OK, let's jump in.
From Windows 7 to Windows 8: The in-place upgrade
In Windows 7, insert the Windows 8 Upgrade media--typically a DVD or USB media key with the installation files--and click through Auto Run to launch the Setup application. After a brief Windows 8 splash screen, Setup begins.
First, choose whether to get any install updates via Windows Update.
Next, enter your 25-digit Product Key. This is required, unlike with Windows 7, though it's unclear if that will be the case in the final version of the product. If you forgot to copy the Product Key that Microsoft provides, you can copy and paste this: It's DNJXJ-7XBW8-2378T-X22TX-BKG7J.
Next, agree to the End User License Agreement, or EULA.
Next, you'll be asked what you'd like to keep. Since you're running Setup from Windows 7, the available choices include "Windows settings, personal files, and more," "just personal files," and "Nothing."
This part of Setup is comprised of technologies that were previously available in the separate Windows Easy Transfer utility. Choose the first if you want to retain (compatible) applications, your personal documents and other data files, and most customizations, and perform what I call an in-place upgrade. Choose the last option if you want to wipe the whole thing out and perform what is essentially a clean install.
Next, Setup will check your system to see whether you need to do anything before proceeding. (Some applications, especially Microsoft Security Essentials, may need to be uninstalled before you can proceed.) If not, Setup will communicate that it's ready to install and verify which things you wanted to keep.
Next, Setup upgrades Windows 7 to Windows 8.
There will be a couple of reboots during which Setup prepares the system, updates the Registry, configures device drivers, applies user settings, and so on.
When this process is complete, Setup will boot into the Out of Box Experience (OOBE), where you make your final system configurations.
First, personalize the Start screen with a color scheme.
Then, choose Express or Custom settings. I've already thoroughly documented the various settings that are applied with the Express choice in other articles in this series, but the short version is that most users should simply choose Express. (I do.)
Then, logon to your previous, Windows 7-based user account.
Here, Setup will allow you to change this logon to an existing (or new) Microsoft ID. I recommend doing so, but if you'd rather not, you can retain your previous local account by clicking "Don't want to sign in with a Microsoft account?"
Supply the password for your Microsoft account.
Enter (or, more likely, confirm) your security verification info, which includes your mobile phone number and an alternate email address.
Then, Setup creates your account, finalizes your settings, prepares Windows, and logs you onto to your upgraded, Windows 8-based PC. Congrats, you're done.