its hard to help you if you can't provide the Theme Name you are using. premium themes have different theme structure. they still have footer.php file but it is probably not in the theme root directory, this is mostly the cases for those theme that has advance features, and its also a very worst idea to edit the file directly if the theme is not in simple structure as you might loss some of the theme features.
if you know a little bit of web development and CSS, use "Inspect Element" and check the element holder of the Content you wanted to git rid off.
in the url you provided, its this one
<div id="footer-bottom"><p id="copyright">Designed by <a href="#" title="Premium WordPress Themes">Elegant Themes</a> | Powered by <a href="#">WordPress</a></p></div>
Now, go ahead and find somewhere you can add a CSS globaly.
and add something like this.
#footer-bottom {
display: none;
}
or
#copyright {
display: none;
}
hope it helps