Comment on Website Navigation Structure SEO Guide by SEO Gold Services.
H* headers are optimized, changing them is generally not a good idea.
I assume you are looking at the home page or categories, the H1 header is used for the title of the site on home and title of a category on categories since they are the most relevant SERPs for those pages. On Posts/Pages the H1 header is the name of the post not the title of the site etc…
It’s generally believed one H1 header per page is best for onpage SEO reasons and you’ll find that’s what you get on every page Stallion generates unless you manually add H1 headers within a Posts content.
If you do want to change the output on the home page archives the files to edit are content.php and content-*.php if you use the Post types like Gallery, Aside etc….