$role_wp = $wpdb->get_var( "SELECT meta_value FROM wp_usermeta WHERE user_id=$user_id AND meta_key='wp_capabilities' LIMIT 1" );
$role_bb = $wpdb->get_var( "SELECT meta_value FROM wp_usermeta WHERE user_id=$user_id AND meta_key='bb_capabilities' LIMIT 1" );
$lvl_s1 = 'a:1:{s:15:"s2member_level1";s:1:"1";}';
$lvl_s2 = 'a:1:{s:15:"s2member_level2";s:1:"1";}';
$lvl_s1bb = 'a:1:{s:6:"member";b:1;}';
$lvl_s2bb = 'a:1:{s:9:"moderator";b:1;}';

if ($role_wp == $lvl_s2) {
    $wpdb->query("UPDATE wp_usermeta SET meta_value='". $lvl_s2bb ."' WHERE user_id=". $user_id ." AND meta_key= 'bb_capabilities' "); }

if ($role_wp == $lvl_s1) {
    $wpdb->query("UPDATE wp_usermeta SET meta_value='". $lvl_11bb ."' WHERE user_id=". $user_id ." AND meta_key= 'bb_capabilities' "); }

?>