(well, true-ish - there are other ways to permanently delete
files, such as the rm command), but I think the OP's problem is rather
more fundamental than that as the files don't seem to be being moved to
trash. Thus the need to drop to a terminal and elevate privileges with
a sudo rm......

Well, not need, this is *Linux* after all and there's *always* more than
one way to do a job, but it's probably the quickest and, in my opinion,
easiest way to do it