The latest posts appear on the home page, you can check out demo to see that.
http://demo.themely.com/novapress/
So I am not sure why you are saying it is not displaying the latest posts, unless you have modified the theme.
You can change the size of the first large image on the homepage but you will need to modify the index.php file in the theme.
Can you add me as an admin to your website so I can log in and have a look?