Hi
In the templates index.php (../templates/j51_[YourTemplate]/index.php you will find the following code which defines the logo..
		<div class="logo_container">		
			<?php if($this->params->get('logoType') == 'image') : ?>
			<h1 class="logo"> <a href="/index.php" title="<?php echo $siteName; ?>"><span>
			  <?php echo $siteName; ?>
			  </span></a> </h1>
				<?php else : ?>
			<h1 class="logo-text"> <a href="/index.php" title="<?php echo $this->params->get('siteName'); ?>"><span>
			  <?php echo $this->params->get('logoText'); ?>
			  </span></a> </h1>
				<p class="site-slogan"><?php echo $this->params->get('sloganText'); ?></p>
			<?php endif; ?>
		</div> 
Within this code you will see 2 instances of the following which adds the hyperlink, the first for an image based logo, the second for a text based logo..
<a href="/index.php" title="<?php echo $this->params->get('siteName'); ?>">
You can either edit the link to your own taste or remove the <a ...></a> tags completely which would have this code looking link the following..
		<div class="logo_container">		
			<?php if($this->params->get('logoType') == 'image') : ?>
			<h1 class="logo"> <span>
			  <?php echo $siteName; ?>
			  </span> </h1>
				<?php else : ?>
			<h1 class="logo-text"> <span>
			  <?php echo $this->params->get('logoText'); ?>
			  </span> </h1>
				<p class="site-slogan"><?php echo $this->params->get('sloganText'); ?></p>
			<?php endif; ?>
		</div> 
Hope this helps
CiarĂ¡n