Today while working on a project I had to resize hard disk size of one of the virtual machines. The Windows virtual machine was created using veewee. To resize a VM hard disk size, you have to perform couple of steps:
1. Run the $ VBoxManage modifyhd ~/VirtualBox\ VMs/windows2008/windows20081.vdi –resize 20480 command.
2. Follow the steps mentioned in this post http://derekmolloy.ie/resize-a-virtualbox-disk/ to understand how you can use the gparted to allocate the unallocated space.