They say you can not judge a book by its cover, and yet every day people do. They pick up a book, look at the cover, and then are moved to either put it down, turn it over, or open it up just because of how the cover looks. Websites are also judged by their covers and the first impression often comes from the header.
By default, the WordPress header is a simple piece of code. You do not have to get into the code to change the header that comes with whatever WordPress Theme you choose. You set the blog or website title and description in the Administration > Settings > General panel, and WordPress does the rest.
In its simplest form, the WordPress Classic Theme features the header code like this in the wp-content/themes/classic/header.php template file:
<h1 id="header"> <a href="<?php bloginfo('url'); ?>"><?php bloginfo('name'); ?></a> </h1>
The header is set in an h1 HTML tag and features one template tag used with two different options or parameters. You can learn more about these parameters in the documentation for bloginfo(). Basically, the first one displays the URL of the website in a link, and the second one displays the name of the blog or website as set in the Administration > Settings > General panel. When the user moves the mouse over the header title, the header can be clicked to return back to the main or front page of the site as set in the Administration > Settings > General panel.
With the header image in place, it is time to tackle the rest of the header. Open your style.css style sheet file and look for the following:
Your Theme may or may not have all of these, but the Default Theme has all of them in different places within the style sheet. All or some of these may need to have the attributes changed to change the look of your header.
If you change the size of the header image or header art, be sure and change the other structural CSS selectors like content and sidebar to accommodate the change in the header size.