The Idiot Proof Guide for Windows-host, *-guest setup. (Ubuntu in my case, and should work for any host)

  1. Make sure you’re working with a VDI, not a VDMK (if not, File>Virtual Media Manager right-click, Copy)

  2. Drop into a command line (on windows, press Win+R, type ‘cmd’) and navigate to the Virtualbox directory (won’t need to do this on *nix)

  3. Execute VBoxManage _path_to_your.vdi_ --resize _new_size_in_MB_

  4. Download UBCD and mount it as a DVD to your VM

  5. Boot into the live DVD (F12 -> c on Oracle Boot Screen)

  6. Select ‘Parted Magic’, and open GParted once it boots

  7. Manipulate and resize to your hearts content

  8. Reboot and enjoy the space!