What Is Windows-10 Error Code 0xc1900201?

I have 1703 creator on my system. Recently when I am trying to install windows 10 1709 with some security things, it is showing windows-10 error code 0xc1900201. My operator said that the system reserved partition space is small and needs to extend. When I am trying to change the settings, it is not allowing me to do so. What can I do know?

