If you haven't yet downloaded the Windows 10 upgrade, hurry up and do it. Right now, it's free. After July 29, it will cost you $119.

In honor of the operating system's first birthday, Microsoft plans to release an Anniversary Update, which will include improvements to Cortana—the company's voice-activated personal assistant—and drawing functionality with Windows Ink. When that happens, the company will pull the plug on its free Windows 10 upgrade offer for consumers who use PCs that run on Windows 7 or an earlier operating system (users of assistive technologies will still be eligible for the free upgrade after July 29).

And that means you'll be stuck paying the full retail price.

What You Need to Upgrade

To be eligible for the upgrade, you need to have a genuine version of Windows RT, Windows 7, Windows 8, or Windows 8.1 on your PC. Windows XP and Vista don’t qualify.

In addition, Microsoft advises you to confirm that your device is compatible with Windows 10. For links to the support pages for various manufacturers, look here.

You’ll also need at least 8GB of free space on your current Windows PC for the Windows 10 upgrade. If you need to free up room, Microsoft suggests running Disk Cleanup or connecting an external hard drive to your PC.

Want to take Windows 10 for a test run? Go right ahead. (It’s free, after all.) If you don't like the new system, it’s possible to revert back to your old operating system with this list of recovery options, Microsoft says. Of course, you could use this as a great excuse to upgrade from your aging Windows laptop to a new model (or even consider the new MacBook). Just make sure you properly dispose of your old one.

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