Firstly go to this page. Although it’s for testing Windows 10 s on existing education devices, anyone can download the self-installer. Read the information to make sure you understand what you can and can’t do. It’s important to note that while you can install Windows 10 S on devices running other editions of Windows 10 it’s not recommended to do so on a Windows 10 Home device as you won't be able to activate it. You'll also need to be running the Creators Update (1703), or later. The Windows 10 S installer will overwrite your existing version of Windows, which means it could screw things up for you, and obviously it won’t be able to run any non-Windows Store software.