Changing frontpicture on 'Abundant' theme

I’m using the theme ‘Abundant’ for my website, http://www.rawrviking.com, and I’d like to change the big red flower picture to a custom. I have NO clue how.

In the Header.php I found this in the site source text
<div id=”logo”>
<h1>/”><?php bloginfo(‘name’); ?></h1>
<p><?php bloginfo(‘description’); ?></p>
</div>

I then thought that would be what I searched for. I tried and changed the a href to a link to a signature picture I use on forums. All that resulted in, was an error screwing the website.

The theme is downloaded here http://www.freewpthemes.net/preview/abundant/

If someone got an answer, I’d be very grateful.

Best regards, Jonas