Related code you can find in theme folder – library – structure. There is one file for header called
header-extensions.php and one for content called
These tags are used for theme styling so you will have to adjust divs in
style.css because otherwise you broke down the entire thing.
Just FYI, I am involved in SEO for the past 5 years and I can assure that you will be wasting your time by changing tags and divs. Google quit rating them years ago and now it’s all about an actual content. Keywords, descriptions, tags, frames is thing of past and no changes made in theme structure won’t give you anything unless you have few million pages than needs to be crawled by Google bots. Then logical content structure, classification is crucial but just for faster indexing not for positions in Google SERPS.