how to costume title single page

You can use “the_title” filter for this.

http://codex.wordpress.org/Function_Reference/the_title

add_filter('the_title','callbackfunction');
function callbackfunction($data){
   global $post;
   $new_title = "new page title"; //You can set dynamic title from $post
   return $new_title;
}

If you just want to change the site title you can do this in the backend itself

“Settings->General->Site Title”