Resizing Virtual Disk Size Under Virtualbox 4 and Higher

In the earlier versions(< 4), there was not any direct method of resizing the size of virtual box disk however with the release of Virtualbox 4 and higher, the VBoxManage tool can be easily used to resize the vbox disks.

Open the terminal and navigate to the folder that contains your Vbox disk and just type the following command and in few secs, you are done.

VBoxManage modifyhd filename.vdi --resize 30720

The above command will resize the filename.vdi disk to 30 GB(30GB = 30*1024 = 30720).

If you are running virtualbox version less than 4, then you will have to create a bigger virtual disk and then clone the content from the existing virtual disk. You can freely download the disk cloning/backup tools for cloning. I hope this helps.