It's homepage so,
check in your theme folder or via WP-admin panel>appearance>editor for home.php or index.php or page.php;
there should be
<div class="welcome_container"><hr />
<div class="two_third welcome-box">
<h1>Welcome to the home of Kadia - Bournemouth Acoustic Folk Indie Band</h1></div>
<div class="one_third last">
<a class="button large" href="http://www.facebook.com/kadiaband">Like us on Facebook</a>
The code might look different in your php file, but the welcome div should be the same. Your FB link is in there - replace
<a>..Facebook.</a> content with your own code.
This is my suggestion.
(if it's your parent theme after updatng your theme version, you will overwrite php file and lose your changes and should do this again).