How familiar are you with HTML, CSS and WP? What you want to do is quite involved. This thread addresses the question further:
http://wordpress.org/support/topic/twenty-twelve-too-many-h1-tags?replies=11
There are some valid points on this topic in the linked article by WPyogi.
Anyway, the following are some guidelines to change those h1 tags to h2 tags…
– Create a child theme
– copy content.php from parent theme’s directory to the child theme’s directory
– replace all instances of ‘h1’ to ‘h2’ in that file. (actually 4 instances, including the closing tags)
I hope this helps.
BTW, if you do change those tags (from h1 to h2), the site may not look as earlier. So, you may want to play around with the styles of h2 tag to make it look like h1, to bring the original UI.
