How do I link the side images?

I took a look at your site, and are you sure you dont want to make the .wrapper clickable? boxed-layout is your whole site, so if you made that clickable the whole site would be a link.

However, if I look at your question, the answer would be to use jQuery.

<script>
$(".body.boxed-layout").click(function(){
window.location = "http://link/to/other/page/";
});
</script>

Note that this probably is not what you want!

Are you sure you don’t want to make the http://classichits.ie/wp-content/uploads/2016/01/leftside.png clickable?