Hello,
Since the last Google updates, I don't think this will have any ranking impacts. However, you can create a template override.
1. Make folder /templates/hot_restaurant/html/com_content
2. Make folder /templates/hot_restaurant/html/com_content/article
3. Copy file /components/com_content/views/article/tmpl/default.php into the folder from the step 2.
4. Edit file /templates/hot_restaurant/html/com_content/article/default.php and change all instances of <h2> and </h2> to <h1> and </h1>
Regards
Milos