The unnamed section is likely a recovery section or something. I assume you listed them left to right so that makes it first and not much you can do to reclaim it without third party partitioning software. Plus if it does have recovery files you might want it.
Is drive D: empty? Is F: empty? G: empty? I'm going to bet since you call it Data that it is not empty. I am hoping that F: and G: are empty.
What I suggest is this...
The youtube video is correct but I suggest you start with F & G NOT C.
Move all the files off of G: to F: if there are any (or to DVDs or flash drives etc if F: does not have room)
Then Delete G and extend F: as in the video. (so G is gone and F is bigger)
Then you move all your D: Data to F: (If you actually already had any data on F: then make sure to rename any folder names that match those on D: because you need to bring the D: folder structure over exactly as it was). Depending how much data is on D: this may take some time to move all that data.
Then with D: empty you merge C: with D: (Delete D: and Extend C: so D: is now gone as in the youtube video).
Finally you rename F: to D: so none of your programs ever even realize D: is no longer on the same physical drive. To do this go back into Disk Management and select F: with your mouse and then right-click. Choose
Change Drive Letter and Paths. Change it to D:
At this point I would reboot to make sure everything went smoothly.
That should be the solution.
Notes:
Don't run any programs except Windows Explorer while you are fixing this to avoid data not being on the drive where it looks.
FYI my internet service is in and out tonight so I just have to answer when I can