The Creators Update of Windows 10 has put the 30 GB folder C: \ Windows.old on the system partition of my PC. All my attempts to remove that directory with administrator rights via >>Disk Cleanup<< or manually will fail. Windows says that I need 'system' rights for that. How can I get it?
The problem you describe occurs after installing the Creators Update and should disappear by itself ten days later. Then Windows removes the Windows.old folder itself. If that has not happened to you or if you can not wait that long, you can delete the folder in the following way:
Open the >>Settings<< and select >>System<< . Then click in the left menu on >>Storage<< and then on >>This PC (C :)<< . In the next screen you can see how much disk space the various types of files occupy. Click on >>Temporary files<< . Under the heading >>Delete temporary files<< you will find the option >>Previous version of Windows<< . When you check that option and click on the button >>Delete files<< , your hard disk will get some air again.