In lib/tpl/default/main.php, edit:
<div class="header">
<div class="pagename">
[[<?php tpl_link(wl($ID,'do=backlink'),tpl_pagetitle($ID,true))?>]]
</div>
<div class="logo">
<?php tpl_link(wl(),$conf['title'],'name="dokuwiki__top" id="dokuwiki__top" accesskey="h" title="[ALT+H]"')?>
</div>
<div class="clearer"></div>
</div>