As of October 2015, Windows 10 is available as a free upgrade for existing Windows users with computers or laptops that run Windows 7 or Windows 8.1. It is also possible to purchase new laptops and computers pre-installed with Windows 7 or 8.1 and upgrade to Windows 10 for free.
According to Microsoft.com, genuine Windows users have the option to download Windows 10 for free if a copy is reserved within the first year of its release. Windows 7/8 Enterprise OS and Windows RT editions are excluded from the free upgrade offer, so users running these systems must purchase a copy of Windows 10.
Windows.com explains how existing Windows 7 and 8 Home or Professional users can reserve and download a full free copy. To download Windows 10 for free, the computer or laptop must have Windows Update enabled, an Internet connection and more than three gigabytes of space.