Mail Chimp Form Integration

Apart from adding the Mail Chimp API & List ID into "subscribe.php" there's not much information about setting up the data fields in the documentation. I have a sign up form in a mega menu. The fields to be sent to Mail Chimp are First Name, Last Name & Email - in Mail Chimp these are FNAME, LNAME & EMAIL. How do I setup the form to send the data to Mail Chimp, here's the code in the mega-menu:

<ul class="mega-menu-column col-md-4">
<li>
<div class="widget clearfix">

<h4>Sign Up for our Mailing List</h4>

<div class="contact-widget" data-loader="button">
<div class="contact-form-result"></div>

<form class="nobottommargin" name="template-contactform" action="include/subscribe.php" method="post">

<div class="col_full">
<div class="col_full">
<input type="text" name="FNAME" value="" class="form-control required" placeholder="First Name" />
</div>
<div class="col_full">
<input type="text" name="LNAME" value="" class="form-control required" placeholder="Last name" />
</div>
<div class="col_full nobottommargin">
<input type="email" name="EMAIL" value="" class="required email form-control" placeholder="Email" />
</div>
</div>
													
<div class="clear"></div>

<div class="col_full hidden">
<input type="text" id="template-contactform-botcheck" name="template-contactform-botcheck" value="" class="form-control" />
</div>

<div class="col_full">
<button class="button button-3d button-small nomargin" type="submit" id="template-contactform-submit" name="template-contactform-submit" value="submit">Sign Up</button>
</div>

</form>
</div>

</div>
</li>
</ul>

Is there anything else that needs to be added/changed on the subscribe.php file to make this work?