Insert this php code in your template’s index.php file just before the closing </head> tag
hint: make sure it’s inside: <?php … ?>
$document = &JFactory::getDocument();
if (JURI::root() == JURI::current()) { // Front Page
? $document->setTitle( "Your Front Page Title" );
} else { // All other pages
? $document->setTitle( $document->getTitle() . " ? Your Site Name" );
}