jComments is free and popular Joomla extension for adding commenting system in Joomla. However, this extension displays a link to joomlatune website.
This tutorial works for jComments 2.3.0 version for Joomla 2.5.
To remove the footer link, open the folder components/com_jcomments/tpl/default/ and edit the file tpl_index.php
Find (use ctrl + F) and remove the following lines of code:
<div id="comments-footer" align="center"><?php echo $this->getVar('support'); ?></div>