Page title unable to overwrite default title
function mytheme_preprocess_page(&amp;$variables) {

  if (!empty($variables['page']['content']['system_main']['#form_id']) &amp;&amp; $variables['page']['content']['system_main']['#form_id'] == 'form_id') {
    if (arg(0) == 'node' &amp;&amp; arg(2) == 'node-type') {
    drupal_set_title(t('Your title'));
    }
   }
 }


you can use dpm($variables) to find form id. This for changing page title.

For changing header title i.e the title displaying in tab, below code can be used

function mytheme_preprocess_html(&amp;$vars) {
  if (!empty($vars['page']['content']['system_main']['#form_id']) &amp;&amp; $vars['page']['content']['system_main']['#form_id'] == 'your_form_id') {
    $vars['head_title'] = t('title');
  }
}