open yourtemplate/html/mod_login/default.php
at line 5 to 7 :
<li><a href="<?php echo JRoute::_("index.php?option=com_user&task=logout&return=".base64_encode('index.php'));?>" class="logout-switch"><?php echo JText::sprintf( 'HINAME', $user->get('name') ); ?>
<?php endif; ?>
<?php echo JText::_( 'BUTTON_LOGOUT'); ?></a></li>
replace with:
<li><a href="<?php echo JRoute::_("index.php?option=com_user&task=logout&return=".base64_encode('index.php'));?>" class="logout-switch"><?php echo JText::sprintf( 'HINAME', $user->get('name') ); ?>
<?php endif; ?>
<?php echo JText::_( 'BUTTON_LOGOUT'); ?></a></li>