Making your Post title your H1 tag is a very big deal when it comes to SEO it's because Search engine gives more attention in H1 Tags compare to other heading tags.
If you need more knowledge about heading tags visit: What is Heading Tags and how to use it.
Now i will teach you how to Edit your Theme so it automatically make your Post Tittle an H1 Tag.
So lets start our Step by Step Tutorials in Changing your Post Title to H1 Tag.
Step 1: Go to Blogger>Layout>Edit HTML
Step 2: Click the "Expand Widget Templates Check box"
So its shows all the codes of your Blogger theme
Step 3: Find This Code:
Remember: Bellow that code you will see a code something like this:
As you can see the above code is Optimized. If its happen to to be an <h2> or something, just change it to <h1>
Step 4: Change the CSS Code for the Title Tag.
In Step 3: If you Change an <h2> to <h1> be sure to change the CSS style from <h2> to <h1> also.
This is maybe Difficult for beginners for HTML. Just free to ask Questions and ill answer it.
Hope you understand. :D