Hi Claire,
lines 293 and 294 for the block name inside the blocks admin page,
line 797 for the cheapest products inside the t('') function:
$output .= '<h2 class="title cheapest">'.t('Our Cheapest Products').'</h2>';line 829 for the best sellers products inside the t('') function:
$output .= '<h2 class="title best-sellers">'.t('Our Best Sellers').'</h2>';