I tried resizing my VirtualBox disk (.vdi) with VBoxManage, but it didn't resize the hard drive. The command while in the root folder of VirtualBox was:
VBoxManage modifyhd "C:\Users\<name>\VirtualBox Vms\Linux Mint 14.1\Linux Mint 14.vdi" --resize 30000.
The output showed 0%...20%....40%...100% looking like it was successful. Now my .vdi in VirtualBox shows the virtual size as being 29.30gb, but the actual size is still 7.90gb. When I boot into Linux Mint, it still notifies me that the hard drive is out of space.