It's one of the less delightful aspects of Windows (there are a few!).
You will, I suspect, find that there is only one folder and that both "C:\Documents and Settings\Groucho" and "C:\Users\Groucho" contain exactly the same items. Delete a file from one, and it will be gone from t'other.
As mixture says, there's an old symlink in there that tells it "if he asks for this, point him at that". The symlink itself takes up all of about 4k on your machine (at worst). You can delete it (if you can find it), but it won't do a lot of good. You might break something that worked and have more fun trying to sort that.
You may also find that in "C:\Users\Groucho" you have two identical folders called "My Documents". Again, there's probably only one on your PC but a leftover symlink.
It doesn't matter until you come to doing a backup (with something like robocopy, see different thread). Then, the copy routine will copy twice. If you're unlucky and the symlink was badly written, then it will go into a loop and try to copy an infinite number of times with sad effects on your backup drive capacity.
I got round that with a "don't follow symlinks" command in my drive C backup routine.
I wouldn't delete the "Documents and Settings" folder!
If you're short of drive space, you could put in a different hard drive and have Win 10 boot to that one.