Need To Undo This

[dieselpowered]

Hi there, could someone please tell me how to undo this:

require_once('./global.php');

echo '<font face="Verdana" size="2">Creating the settings table<br>';
$DB_site->query("CREATE TABLE `" . TABLE_PREFIX . "rss_settings` (`enabled` tinyint(1) NOT NULL default '1' );");
echo '<font size="1">successful!</font><br><br>';

echo 'Creating the users table<br>';
$DB_site->query("CREATE TABLE `" . TABLE_PREFIX . "rss_user` (`rssuserid` int(10) NOT NULL auto_increment, `userid` int(10) NOT NULL default '0', `forumid` smallint(5) NOT NULL default '0', `source` varchar(150) NOT NULL default 'http://news.com.com/2547-1_3-0-5.xml', `enabled` tinyint(1) NOT NULL default '1', PRIMARY KEY  (`rssuserid`));");
echo '<font size="1">successful!</font><br><br>';

echo 'Modifying the threads table<br>';
$query = $DB_site->query("ALTER TABLE `" . TABLE_PREFIX . "thread` ADD `rss_feed` TINYINT( 1 ) DEFAULT '0' NOT NULL, ADD `rss_date` VARCHAR( 35 ) NOT NULL");
echo '<font size="1">successful!</font><br><br>';

echo 'Inserting data into settings table<br>';
$DB_site->query("INSERT INTO " . TABLE_PREFIX . "rss_settings (enabled) VALUES ('1')");
echo '<font size="1">successful!</font><br><br>';