It's part of the larger Extended partition and you will not be able to delete the Free Space; but you would be able to use Option One
of this tutorial to convert it to a Primary partition that can then be deleted and the C: can be extended
Partition Wizard : Use the Bootable CD
As good and reliable a program as Partition Wizard is, I would not trust the installed version for the operation you need, use the boot CD as suggested and be sure to post back with any further questions you may have and to keep us informed.
First download the Partition Wizard Bootable Disk (PWBD) ISO file to the desktop, be sure to get the PWBD and not the installed version; scroll down to see the download link for the Bootable CD ISO file at this link below.
Partition Wizard Free Bootable CD
Then use ImgBurn to burn the ISO to a CD, at no greater than 4x speed with a verify; it was designed for use and works best from a CD rather than a DVD; then boot
the created CD to make the changes, it doesn't take any input from the user to setup, just relax and let it load.
ImgBurn Free ISO Burning Software