How to update a usergroup?

[reteep]

Hi there,

I'd like to manually update a usergroup based on a querystring value:

PHP Code:

define('THIS_SCRIPT', 'addvb.php');

require_once('./global.php');
require_once('./includes/class_dm.php');
require_once('./includes/class_dm_user.php');

$uid = $_GET['uid'];

// init data manager
    global $vbulletin;
    $vbulletin->userinfo = $vbulletin->db->query_first("SELECT userid, usergroupid, membergroupids, infractiongroupids, username FROM vb3user WHERE userid = '" . $userid . "'");
    $userdata =& datamanager_init('User', $vbulletin, ERRTYPE_ARRAY);
    $userdata->set('userid', $uid); // 
    $userdata->set('usergroupid', 2); // Move into Regged UserGroup
    $userid = $userdata->save(); 


However, this is trying to create a new user. In fact I just want to update the usergroup of a given userid. Unfortunately there's no $userdata->update();

I'd appreciate a little help, thanks!