Just look through the index.main.php for

<div id="rightsidebar">
<p class="center">
<!-- Please help us promote b2evolution and leave this link on your blog. --><a href="http://b2evolution.net/"
title="b2evolution: next generation blog software"><img src=
"../../rsc/img/powered-by-b2evolution-120t.gif" alt=
"powered by b2evolution free blog software" title=
"b2evolution: next generation blog software" width="120" height=
"32" border="0"></a></p>
</div>

and comment it out or delete it.

Thanks for the pointer!