If you have a PC running a "genuine" copy of Windows 7/8/8.1 (properly licensed and activated), you can follow the necessary steps to upgrade it to Windows 10.
Windows 10 is a major version of the Microsoft Windows operating system that was released on July 29, 2015. It is built on the Windows NT kernel and follows Windows 8.
Part of the reason Microsoft decided to name the 2015 release "Windows 10" (and skipped "Windows 9") is because the operating systemis designed to be a new direction for Microsoft. One of the primary aims of Windows 10 is to unify the Windows experience across multiple devices, such desktop computers, tablets, and smartphones. As part of this effort, Microsoft developed Windows 10 Mobile alongside Windows 10 to replaces Windows Phone – Microsoft's previous mobile OS. Windows 10 also integrates other Microsoft services, such as Xbox Live and the Cortana voice recognition assistant.
While Windows 10 includes many new features, it also brings back the Start Menu, which was dropped in Windows 8. The new and improved Start Menu provides quick access to settings, folders, and programs and also includes tiles from the Windows 8 interface. The bottom of the Windows 10 Start Menu includes a search bar that allows you to search both your local PC and the web.
Another major change in Windows 10 is the introduction of the "Edge" web browser, which is designed to replace Internet Explorer (IE). While the OS still includes IE, Edge is the default browser in Windows 10. Other new features include Continuum, which automatically optimizes the user interface depending on whether you are using an external keyboard or touchscreen, and Action Center, which is similar to the Notifications bar in OS X. Windows 10 also supports multiple desktops on a single monitor and provides Snap Assist, a feature that helps organize windows on the screen.