title: kubuntu 14.04 to full screen via virtual box
body: <p>I installed kubuntu 14.04 via VirtualBox. 
  I tried to change the resolution via the settings, but I have only one option there: 640X480.
  I understood that I need to install guest additions, but when I try to do so from 
  "Devices"->"insert guest additions CD image", I get this message:
  "unable to insert the virtual optical disk c..."</p>
  
  <p>how can I change the resolution to full screen?</p>