Hi,

In the index.html you can find the code below:

        <!-- BEGIN FOOTER -->
        <footer id="footer" class="section" role="contentinfo">
            <div class="container">
                <ul class="social">
                    <li><a href="#" class="icon tw"><i class="fa fa-twitter"></i></a></li>
                    <li><a href="#" class="icon fb"><i class="fa fa-facebook"></i></a></li>
                    <li><a href="#" class="icon in"><i class="fa fa-pinterest"></i></a></li>
                    <li><a href="#" class="icon go"><i class="fa fa-google-plus"></i></a></li>
                </ul>
            </div>
        </footer>
        <!-- END FOOTER -->

Then change the class in below:

fa-twitter
fa-facebook
fa-pinterest
fa-google-plus

With the icon in here: http://fontawesome.io/cheatsheet/