To change or remove the "Joomla! is Free Software released under the GNU/GPL License." links from the joomla administration area we need to edit 3 files:

administrator/templates/khepri/cpanel.php
administrator/templates/khepri/index.php
administrator/templates/khepri/login.php

cpanel.php

This file displays the branding on the main admin page.

Search for the lines:

<p class="copyright">
<a href="http://www.joomla.org" target="_blank">Joomla!</a>
<?php echo  JText::_('ISFREESOFTWARE') ?>
</p>

Either delete these lines or change the link and text and delete the php line.

index.php

This file displays the branding on all other admin pages.

Again, search for the lines:

<p class="copyright">
<a href="http://www.joomla.org" target="_blank">Joomla!</a>
<?php echo  JText::_('ISFREESOFTWARE') ?>
</p>

Modify or delete.

login.php

This file displays the branding on the login page, and is also where you can edit the "Joomla Administration" text.

Once again, search for the lines:

<p class="copyright">
<a href="http://www.joomla.org" target="_blank">Joomla!</a>
<?php echo  JText::_('ISFREESOFTWARE') ?>
</p>

Modify or delete.

Then search for the line:

<h1><?php echo JText::_('Joomla Administration Login') ?></h1>

Edit "Joomla Administration Login" to the name of your website, or whatever you would like to be displayed.

Save all the files and upload to your server.