Open below file for edit:
/storefront/view/default/template/pages/product/product.tpl
Locate below code:
<div class="tabs">
<a rel="#tab_description">
<span class="tab_right"></span>
<span class="tab_left"></span>
<span class="tab_text">
<?php echo $tab_description; ?>
</span>
</a>
<?php if ($review_status) { ?>
<a rel="#tab_review">
<span class="tab_right"></span>
<span class="tab_left"></span>
<span class="tab_text">
<?php echo $tab_review; ?>
</span>
</a>
<?php } ?>
<a rel="#tab_related">
<span class="tab_right"></span>
<span class="tab_left"></span>
<span class="tab_text">
<?php echo $tab_related; ?>
(<?php echo count($related_products); ?>)
</span>
</a>
Change to:
<div class="tabs">
<?php if ($review_status) { ?>
<a rel="#tab_review">
<span class="tab_right"></span>
<span class="tab_left"></span>
<span class="tab_text">
<?php echo $tab_review; ?>
</span>
</a>
<?php } ?>
<a rel="#tab_description">
<span class="tab_right"></span>
<span class="tab_left"></span>
<span class="tab_text">
<?php echo $tab_description; ?>
</span>
</a>
<a rel="#tab_related">
<span class="tab_right"></span>
<span class="tab_left"></span>
<span class="tab_text">
<?php echo $tab_related; ?>
(<?php echo count($related_products); ?>)
</span>
</a>