These are the steps to increase the virtual hard drive size of a VirtualBox machine. These worked for me in Ubuntu linux, but the command should work for Windows as well I believe.
EDIT: Reader recuperar arquivos confirms that this also works in Windows.
Snapshots aren’t supported so first you’ll need to clone the current snapshot into a new machine. Once that’s done, open up a terminal window and type this:
vboxmanage modifyhd “/file/location/of/virtual/harddrive.vdi” –resize 40960
(that “resize” flag needs a double-hyphen in front of it, not just one)
40960 MB = 40 GB
If you want to resize to say, 100GB, you’d use 102400 at the end.
Any questions feel free to leave a comment!