If you ever have the need to change the theme for all your users then this script will help you.

Steps :
Create a php file and name it updatetheme.php and place it inside your nuke root folder (where config.php and mainfile.php are located). Place the following codes inside that file.

<?

require_once("mainfile.php");
global $user_prefix, $db;

$result = $db->sql_query("UPDATE ".$user_prefix."_users SET theme='YOURTHEMENAME' WHERE user_id !='1'");

if(!$result){
echo 'User themes not updated';
}else{
echo 'User themes updated successfully';
}
      
?>

Change the YOURTHEMENAME to the actual name of the theme you want everyone to use. Run that file in your browser http://www.yoursite.com/updatetheme.php .

That's it! Enjoy and please Back Up as usual before making any major changes.