How to extend Windows 7 VM disk size on VirtualBox v4.2.16

Problem:

The 30GB C: drive was running out of free space on my Windows 7 VM guest on VirtualBox v4.2.16.

Solution:

1. Shutdown VM.

2. Extend it to 45GB:

$ cd /home/user/.VirtualBox/HardDisks

$ VBoxManage modifyhd windows7.vdi --resize 46080
0%...10%...20%...30%...40%...50%...60%...70%...80%...90%...100%

3. Extend partition size in Windows 7

a. Start the VM


b. Run diskmgmt.msc > right-click C: > Extend Volume...