Note: Take a backup of your vDisk (.vhd)
Open Comand Prompt or Powershell and get Diskpart
On Diskpart enter "Select vDisk file=
Enter "List vDisk"to check if the vDisk has been added or not.
After that Expand the vDisk by using following query "expand vDisk maximum=61440 (in Mb)". The size should be in "MB"
On Diskpart enter "attach vDisk" to attach it. Type "list disk" to check if the vDisk has been attached.
Type "List Volume" to see what are the available volumes
Type "Select Volume 3" the vDisk which you want to resize and enter "Extend" to extend the vDisk.
Note: The number of the vDisk you want to resize
Now the vDisk has been extended to verify type "List Volume" to see the status. after checking the status. Type "Detach" to detach the vDisk.