VirtualBox - How to extend/enlarge/grow your windows vm vdi hard drive

(1) Run this command line to grow to 100 GB

VBoxManage modifyhd HARD_DRIVE_FILE_NAME.vdi --resize 100000

(2) Open windows "Disk Management" app and right click over the hard drive you are trying to grow, and select "Extend". Follow the menu prompts (default selections work), and voila!