Simply change the background-image:url('images/your-image.png');
inside of the markup to your image and you are good to go.
<!--=== Begin Header Parallax ===-->
<div class="header-parallax" style="background-image:url('images/backgrounds/bg3.jpg'); background-color: #272727;" data-top-bottom="background-position: 50% 0px;" data-bottom-top="background-position: 50% -200px;">
<div class="container">
<div class="row">
<!--=== Page Title ===-->
<div class="col-lg-6 col-md-6 col-sm-6 col-xs-12">
<h1>Header Parallax</h1>
<p class="text-white">Hi, I am a parallax header; go to the parallax page to learn how to change my direction.</p>
</div>
<!--=== Breadcrumbs ===-->
<div class="col-xs-6 pt30">
<ol class="breadcrumb text-white link-white">
<li><span class="ion-home breadcrumb-home"></span><a href="index.html">Home</a></li>
<li>Features</li>
<li>Header 1</li>
</ol>
</div>
</div><!-- /row -->
</div><!-- /container -->
</div><!-- /page header -->
<!--=== End Header Parallax ===-->