Unable to resize Bootcamp partition containing Windows 10 Pro

I have a MacBook Pro (2016) with a 500GB SSD. On the SSD is the MacOS High Sierra occupying 250GB, and Windows 10 Pro occupying about 200GB. All I want to do is to increase the size of the Bootcamp partition where Windows is located to about 250GB. I need to do it non-destructively -- don't want to reinstall Windows and associated programs (too difficult and time-consuming). I read that this program can do that, but I can't find anything about this in the User Manual. Does anybody know how to do this, or point me in the right direction (even if it's another program)? And, while I'm here, why are the Forum posts in German? Can't select English.