Changing h tags for SEO?

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I can′t seem to find the way to change the h tags.

I want the site title to have the H1 tag on the home page ONLY.
on the homepage the post titles should have h3.

I want the post titles to have H1 on the single post pages.

I want the category title on the category pages to have the H1 tag and the post titles of that category H2.

I don′t want the widgets to have H3 tags or higher.

All in all a good theme but not optimized for basic SEO. And it seems you can′t change it either.