Note: This guide will be updated throughout the day as I perform more upgrades and respond to feedback. Let me know if you see anything missing.

With Windows 8.1 now generally available, it's time to upgrade. Fortunately, Windows 8.1 is the easiest Windows upgrade yet, and that's especially true for Windows 8 (and RT) users. Here's a complete guide to upgrading to Windows 8.1 using electronic media.

I'll discuss upgrading via DVD media in a future article. This article focuses on the electronic upgrade, which occurs through various online means (depending on which version of Windows you're starting with). I've gotten a lot of questions about an ISO version of the upgrader, but that doesn't exist: Those who have access to an MSDN or TechNET subscription can install Windows 8.1 in that fashion, as can those who purchase a Full Windows 8.1 product online or on DVD.

Note: For a more visual look at the upgrade process, check out Windows 8.1 Upgrade: Step-By-Step.

Windows 8 Core/Pro or Windows RT (RTM)

Cost: This upgrade is free.

Upgrade type(s) available: You can perform a complete upgrade, meaning that you can choose to bring your desktop applications, Metro apps, settings, and personal files forward to the new OS version.

Open a web browser and visit windows.com/buy. Click the "Get the Update" button, and Windows Store will launch to the landing page for the Windows 8.1 upgrade. (If this isn't working for some reason, you can force this page to load by using IE to navigate to ms-windows-store:WindowsUpgrade.)

Click on the Update Windows tile, and then the Download button. The installer (2.81 GB for the 32-bit version) will download. You can view the progress on the Installs page in the Store app if you want. But it will eventually prompt you when it's time to install.

Installation occurs offline and will trigger a few more reboots. When you boot back into the Welcome screen, Windows RT 8.1 has been installed and you're good to go. (And can reinstall your apps.)

Windows 8 Enterprise

If you are running Windows 8 Enterprise, you will need to check with the source that provided you with the OS—Microsoft Volume Licensing, MSDN, TechNet, or whatever—to obtain Windows 8.1.

Windows RT (RTM)

Cost: This upgrade is free.

Upgrade type(s) available: You can perform a complete upgrade, meaning that you can choose to bring your Metro apps, settings, and personal files forward to the new OS version.

Launch the Store app and click on the Update Windows tile, and then the Download button. The 2.11 GB installer will download in the background and will prompt you over time via a series of full-screen notifications.

Eventually, your RT device will need to reboot to install the update. The installation occurs offline and will trigger a few more reboots. When you boot back into the Welcome screen, Windows RT 8.1 has been installed and you're good to go. (And can reinstall your apps.)

Windows 8/RT with Windows 8.1 Preview

Cost: This upgrade is free.

Upgrade type(s) available: You can perform a partial upgrade, or migration, meaning that you can choose to bring your settings and/or personal files forward to the new OS version, but not any previously installed desktop applications or Metro-style apps.

Launch the Store app and click on the Update Windows tile, and then the Download button. The 2.11 GB installer will download in the background and will prompt you over time via a series of full-screen notifications.

Eventually, your RT device will need to reboot to install the update. The installation occurs offline and will trigger a few more reboots. When you boot back into the Welcome screen, Windows RT 8.1 has been installed and you're good to go. (And can reinstall your apps.)

Windows 7

Cost: $119.99 for Windows 8 "Core," $199.99 for Windows 8 Pro

Upgrade type(s) available: You can perform a partial upgrade, or migration, meaning that you can choose to bring your settings and/or personal files forward to the new OS version, but not any previously installed desktop applications. Windows 7 users should consider upgrading to Windows 8 first, if possible, since that upgrade will allow them to retain their desktop applications. Then, you can upgrade from there to Windows 8.1 for free.

To get started, launch the Windows 8.1 Upgrade Assistant. (This is not available at the time of this writing.)

Windows Vista or Windows XP

Cost: $119.99 for Windows 8 "Core," $199.99 for Windows 8 Pro

Upgrade type(s) available: You can perform a partial upgrade, or migration, meaning that you can choose to bring your settings and/or personal files forward to the new OS version, but not any previously installed desktop applications. Windows 7 users should consider upgrading to Windows 8 first, if possible, since that upgrade will allow them to retain their desktop applications. Then, you can upgrade from there to Windows 8.1 for free.

You cannot use an electronic install method to upgrade from Windows Vista or XP to Windows 8.1. Instead, you must first upgrade to Windows 8 or use the retail, DVD-based media described below.

Troubleshooting notes

A few troubleshooting notes...

Make a restore/repair disk before upgrading. To be safe, you should make a restore/repair disk before upgrading to Windows 8.1. I've written about this in many places, but Windows 8 users should check out Windows 8 Tip: Create Recovery Media and Windows 8 Tip: Easily Access Recovery Options.

Get up to date. Before attempting the Windows 8.1 Upgrade, make sure that your current Windows version is up to date. This means visiting Windows Update, of course, but also Windows Store if you're using Windows 8/RT. Don't try upgrading until everything is up to date.

Windows RT issues. It's hard to pin down why this is so, but I've had a much harder time getting Windows RT updated on Day One than I did with Windows 8. Keep trying, or just give it some time: It seems like the issues are all Windows Store related, and it could just be related to the volume of requests.

Make sure your PC is tied to your account. When you sign in with a Microsoft account, the PC is tied to your account for sync purposes. If the PC you're trying to upgrade isn't tied to your account, you won't see the Upgrade option in Windows Store.

Free disk space. Microsoft says you need at least 10 GB of free disk space to install Windows 8.1.

Did I miss anything? Let me know, and I'll update this article.