I recommend creating a bootable usb/disk of Ubuntu and using gparted from it to do the dirty work.
From personal experience, gparted can not reallocate space from an active partition. I am sure this should work, so long as you delete the partition, then expand Drive C to your desired size.
SOURCE: I did this last week.
*Sidenote: If there is a partition between the two sectors and you find yourself stuck because you cannot move it, Try EaseUS. Should that fail, backup the data on the drive(s) between Drives C and D and delete partition sda2 (ubuntu, sadly) and Drive D. This is a last resort, deleting ubuntu's partition, but there are programs for ubuntu that can create a backup installation, so you lose no programs. Then move the amount of space equal to D to C and reallocate Ubuntu's Partition when finished.
Should you have any issues with your MasterBootRecord (MBR), use a Windows Install Disk (Repair)(if you can not boot into Windows), Ubuntu Boot Repair (LiveCD)(if you can not boot into anything), or EasyBCD (if you can boot into Windows, but not Ubuntu).
Good Luck.