Download and replace files. http://themes.tvda.eu/demos/kutcherstudio/usernametweet.zip

Change (index.html):

<script src="https://api.twitter.com/1/statuses/user_timeline/twitter.json?callback=twitterCallback2&count=1"></script>

to

<script src="https://api.twitter.com/1/statuses/user_timeline/YOUR_USERNAME.json?callback=twitterCallback2&count=1"></script>

If you do not want to replace the index.html. Change code of Parallax2 section (in index.html):

<!-- Start Second Parallax Background (Twitter) -->
<div id="parallax2">
    <div class="bg2" />
    <div class="pattern" />
    <div class="container">
        <div class="eleven columns">
            <div class="vertical-text">
                <div id="lasttweet" />
                <img alt="" src="images/social-icons/follow.png" style="margin-top: 36px;" />
            </div>
        </div>
    </div>
</div>
<!-- End Second Parallax Background (Twitter) -->

And add script to the bottom of the page (before )

<script src="https://api.twitter.com/1/statuses/user_timeline/YOUR_USERNAME.json?callback=twitterCallback2&count=1"></script>