How can I change the title tag in header of just one page?
You can manage this in template.php file.

function MYTHEMENAME_preprocess_page(&amp;$vars) {
    $vars['title'] = $custom_title;
    $vars['head_title'] = $custom_title;
}


Just put the condition in the page like for specific path, content type etc. and change the title of the page.

function mytheme_preprocess_page(&amp;$vars){
    if (isset($vars['node']) &amp;&amp; $vars['node']-&gt;type == 'news'){
        drupal_set_title('News');
    }
}