01. Launch 'Terminal' ('/Applications/Utilities/' folder).
02. Enter ...
rm -rf
... press the spacebar once.
03. Drag the icon of the item (file, folder, or combination) onto the 'Terminal' window.
04. Click on the 'Terminal' window, and press the <return> key.
05. Quit 'Terminal'.
If the above fails, use
sudo rm -rf (and the spacebar)
... in Step 02. above. You will be asked for the administrator's password, before the 'rm' command is executed.