Using Windows as a Host
Open the command prompt and enter:
# <Path to VirtualBox installation>\VboxManage.exe modifyhd YOUR_HARD_DISK.vdi --resize SIZE_IN_MBEx:# C:\Program Files\Oracle\VirtualBox\VboxManage.exe modifyhd Windows.vdi --resize 20480
Using Mac as a Host
Open a Terminal and type:
# /Applications/VirtualBox.app/Contents/MacOS/VBoxManage modifyhd YOUR_HARD_DISK.vdi --resize SIZE_IN_MB
Using Linux as a Host
Open a Terminal and type:
# VBoxManage modifyhd YOUR_HARD_DISK.vdi --resize SIZE_IN_MBSIZE_IN_MB should be 20480 for 20GB
If you get an error mentioning the VirtualBox COM server, start the VirtualBox Dashboard and make sure you have Administrator rights (command prompt as Administrator / not sure about Mac / sudo in Linux), then try again.
