It seems like the order of KB articles in the Help Center is "older on top", which is not convenient. It is at the categories level and also at the articles level.
The only way to change that is to sort the articles manually. Ideally, there would be a default order with newest articles on top. If not possible, this would be at least interesting that the new articles come on the top of the list (and not at the end, just like the post news), and then can be manually moved.