Oh, my goodness. It's just been pointed out to me that all my page titles (Post Headers) that I've put into my numerous sites are not H1 headers. I'm beside myself. Why?

Hi My heading 'This is No Ordinary Shop' on the page below is H2 but all headings need to be H1 https://noordinaryshop.com/ How do I change the headings from H2 to H1? Thanks