Using Windows Disk Management to extend a NTFS partition

First, backup your data.

1. Shutdown the VirtualBox VM.
2. Open “File” then “Virtual Media Manager”.
3. Select the VDI you want to expand.
4. Increase it’s size.
5. Apply those changes and boot the VirtualBox VM back up.
6. Open Windows “Disk Management” by typing it into the start menu.
7. Right click on the “(C:)” partition and click “Extend Volume”.
8. Use the arrows to max out the value for “Select the amount of space in MB:”
9. Hit next and finish.
10. You should now have a extended guest OS partition.