Save User programitically

 global $user;

$existingUser = user_load($user->uid);

$existingUser->name = $_REQUEST['user_name'];

$existingUser->mail = $_REQUEST['user_mail'];

$existingUser->init = $_REQUEST['user_mail'];

if(!empty($_REQUEST['user_pass'])) {

$existingUser->pass = $_REQUEST['user_pass']; 

}

user_save((object) array('uid' => $existingUser->uid), (array) $existingUser);