For the first time in the history of Windows, Microsoft is making the upgrade to Windows 10 absolutely free for consumers. There are a few requirements but overall it is a very good offer. First, you must be running a fully activated and up-to-date version of Windows 7 or Windows 8. That means you must be running Windows 7 SP1 and Windows 8.1. A consumer edition is also required such as Home or Pro. Sorry Enterprise Edition users. Your hardware must also meet the minimum requirements for Windows 10, which are very low. Finally, you must request you free upgrade within one year of the release of Windows 10 (July 29th 2016).
Requesting the free upgrade is very simple, in fact, the reservation tool will show up on your PC as part of your normal Windows Updates. Simply click on the Windows flag logo that should appear on the right side of the taskbar (near the clock) to open the reservation app. Click the Reserve your free upgrade button and optionally enter your e-mail address for confirmation.
If you can't find the Windows flag logo on the right of your taskbar, take a look at the Windows 10 FAQ.
Windows 10 will automatically download in the background (approximately 3GB download). The reservation application will notify you when it is ready to be installed (after July 29th - Windows 10 launch day).