paulwpxp on "Full Width Header Issue"

The theme you are using hasn't been update for years, and it seems that theme author has been missing too. So I would suggest changing theme, there are plenty of good themes that keep up with recent WordPress update.

So anyway, since this theme has fixed width layout, we can simply make the header area fixed width and assign our big logo as background image.

To do this, first we need to install a Custom CSS plugin, pick one that is simple and install and activate it
https://wordpress.org/plugins/search.php?q=custom+css

Upload the big logo image (960x300) via Media Library, just upload the image and get the image URL. Once we have our image URL, replace the image URL in this code and use the code in Custom CSS

.site-logo { display: none;
}
#header a { background: url("http://dummyimage.com/960x300/eeeeee/000000.png") repeat scroll 0 0; display: block; height: 300px; width: 960px;
}