Microsoft offers downloads of Microsoft Windows 10 Technical Preview for free. Choose the appropriate download link and use product key "NKJFK-GPHP7-G8C3J-P6JXR-HQRJR" to install it. The new interface includes the Continuum feature, which allows users to switch easily between touch and non-touch environments, and Cortana, the personal digital assistant.
Note that early builds carry risks and may not be compatible with all drivers. To return to an earlier version of Windows, you'll need to reinstall the old version.