code: public function run35Update()
  	{
  		$this->Database->query("ALTER TABLE `tl_member` CHANGE `username` `username` varchar(64) COLLATE utf8_bin NULL");
  		$this->Database->query("UPDATE `tl_member` SET username=NULL WHERE username=''");
  		$this->Database->query("ALTER TABLE `tl_member` DROP INDEX `username`, ADD UNIQUE KEY `username` (`username`)");
  	}
docs: Version 3.5.0 update