To re-order articles on an article block:
Click the edit button circle that appears in the bottom left corner of your browser screen when you are logged in and viewing your portfolio.
The button appears at the top of the article block on the page, next to the add article and edit block buttons.
Change the 'Default Order' dropdown. If you want your articles to appear in date order this is all you need to do. If you want to set a custom order you should set it to be "Featured".
Use the drag icon on the left of each article to drag and drop the articles into the order you want.
Note that if your articles block is a masonry grid of articles, the articles are filled by adding them to the shortest column. This means the exact order they appear might vary slightly, especially further down the page.