Post title didn't use h1 tag on single page view

Please, could someone help me overcome this problem? I am newbie and just know basic html and css.

In the home page, the heading tag is right. I see the blog name use h1 and post title h2 on home page, but I see the blog name still use h1 tag and post title h2 tag on single page view. I have try to change it on single.php file and h1 would become two pieces which one is blog name, another one is post title.

I try to googling about this theme customization on its heading tag, but none result.
I know h1 tag is useful for SEO, I really like this theme and hope to use it on my next portfolio.

Any comments or response would greatly appreciated. Thanks.