Hey there, Mark_107.
Unfortunately I don't think you can do that without 3rd party software. For you to be able to extend a partition, the unallocated space should be on the right side of the partition you wish to extend, right next to it. Actually you can do that natively with Windows, but only for secondary drives as it will turn the disk to dynamic and dynamic drives can't be used for boot. So the bottom line is that in your case you'd have to find a 3rd party partition manager with which to extend your C: drive.
Note that this is a bit risky sometimes and you should definitely backup any important data which you might have on that drive, just to be on the safe side.
Hope that helps. Please let me know if you have any questions...