Accessing all the themes is easy to do once you know where to find them. The trick is to navigate to the C:\Windows\Globalization\MCT directory. The MCT directory within the Globalization directory is super hidden so it will not display even if show hidden files and folders is enabled. Just click on the address bar of any folder and manually type in or copy and paste in C:\Windows\Globalization\MCT and hit Enter.
Once you have reached the MCT folder you will see five directories as listed below: