How to edit personal contact form e-mail content - Drupal 7
I don't believe that this can be done through the admin panel though it is quite easy through a module using hook_mail_alter()

if it is the drupal core contact form then use this in YOUR_MODULE.module

function YOUR_MODULE_mail_alter(&amp;$message) {
  if ($message['id'] == 'contact_page_mail') {
    //MODIFY THE MESSAGE HERE
  }
}


(always remember to clear caches after adding a hook)

It is a good idea to get the devel module and add

dpm($message);


see what the variables are that you want to modify and enjoy.