Changing layout on product and making font bigger

You need to go in the menu Display->Views and edit the file listing_img_title of the view product. There you can move the code:
<span class="hikashop_product_name">
<?php if($this->params->get('link_to_product_page',1)){ ?>
<a href="<?php echo $link;?>">
<?php }
echo $this->row->product_name;
if($this->params->get('link_to_product_page',1)){ ?>
</a>
<?php } ?>
</span>

at the top of the file.

If you want to change the font size of the product name, you can go in the config under the tab display and edit your CSS and add something like this:
.hikashop_product_name{ font-size: 2em; }

Are you sure that you edited the correct file ?

You can use:
line-height: 1em;

No, you can't have two groups of brackets in CSS. It should be:
span.hikashop_product_name{ font-size: 2em;
line-height: 1em;
}