I noticed this on one of our VM's where it is one virtual disk with three partitions, I cannot expand the C: partition. If you copy all of your data off of D: and delete the partition, you will be able to extend your C: Drive to your hearts content, then you can recreate and copy back the data to your D.
You wont be able to extend your C: with D: on the same drive. If that's not an option, you can move partitions about with gparted.
From the looks of it, you installed gParted to the vDisk, rather than using it as a outside tool to the vDisk. I am running out of space on my C drive, running a windows R2 VM.
