@Clems26: I don’t see multiple H1 in your site. Also which H1 are you trying to change it. You can change it by building child theme and editing it.
Also only one H1 per page is old. It was only valid for HTML4.
In HTML5, you can have more then one H1 tag. That was issue only when you use HTML4 tags. In HTML5, H1 tag per article tag is good for SEO and we have carefully designed H1 tags with special attention on header tag and headings
Catch Everest theme is build in HTML5, CSS3 and Responsive design. So, H1 is better for SEO then H2.
You can also check this Video http://www.youtube.com/watch?v=GIn5qJKU8VM by Google software engineer Matt Cutts, who clearly states that you can use multiple H1 but don’t over do it. Also use h1 specific to heading and header tags.
You can also check this article URL http://html5doctor.com/html5-seo-search-engine-optimisation/