In file includes/frontend.php:

Replace
$mainframe->addMetaTag( 'Generator', $_VERSION->PRODUCT . " - " . $_VERSION->COPYRIGHT.;
With
/**
$mainframe->addMetaTag( 'Generator', $_VERSION->PRODUCT . " - " . $_VERSION->COPYRIGHT.;
**/
Commenting this one.
Or you can Add your own Meta tag with this.
$mainframe->addMetaTag( 'Generator', $_VERSION->PRODUCT . " - " . 'Your Copyright Techtime.com'.;

In files administrator/templates/mambo_admin/index.php and administrator/templates/mambo_admin_blue/index.php:

Remove the following lines:

Then replace
echo "rn";
?>
With
/**
echo "rn";
**/
?>

Simple enough and we didn’t remove the copyright notice from the code.