How to do this depends on your platform:
Windows:
- download the attached file radRnoguiWindows.zip into your radR folder
- unzip that file to obtain radRnogui2.5.1.bat
- from the file manager, double-click on the icon for radRnogui2.5.1
Linux:
- cd to the radR installation directory and do:
R --args --no-gui