By default, Joomla will publish your articles in the order that they were written: So newer articles are always placed at the top of your blog layout, and are replaced with more current articles as you publish them.
To change the order of your articles, select from ARTICLE MANAGER from the CONTENT tab in the top menu. Your page will display a list of articles on your website.
In the graphic below, you can see there are three artcles (Last weeks article, Yesterdays article, and Todays article). Take note of the icon that represents three vertical dots beside each article. The ordering of each article can be changed by dragging the icon up and down into position.