Disable h1 and h2 from rich text editor combobox

In the WordPress control panel, when writing a new post, I would like to disable the Header 1 and Header 2 from the text formatting combobox, because I already use them on my theme (h1 for blog name and h2 for post titles), and would like to keep all headers inside a post with h3 or higher. Is that possible?

It doesn’t matter for the case if the code can be edited in the HTML view. Also, I don’t want to edit WordPress internal files, so a hack for functions.php or a plugin would be great for this task, in order to preserve this change across future updates.

Thank you!

you can change lots of things about the tinyMCE editor at the tiny_mce_before_init filter.

http://codex.wordpress.org/TinyMCE_Custom_Buttons

the following will restrict your blockformats to p,h3,h4 and blockquote

function wpa_45815($arr){
    $arr['theme_advanced_blockformats'] = 'p,h3,h4,blockquote';
    return $arr;
  }
add_filter('tiny_mce_before_init', 'wpa_45815');

EDIT for WordPress 3.9 see link

function wpa_45815($arr){
    $arr['block_formats'] = 'Paragraph=p;Heading 3=h3;Heading 4=h4';
    return $arr;
  }
add_filter('tiny_mce_before_init', 'wpa_45815');