php help

php help

I had a php programmer integrate my forum with my video ripping site which basically set a 20mb download limit for members of the forum and they earn an extra 2mb per post they make within the forum, I’d like to increase this limit from 2mb to 5mb but I cant get hold of him despite sending numerous emails, he always said it was easy to change but I dont understand php so for me its hard. I think I’ve found the section of code I need to change but could someone explain what this section of code means:

$numPosts = mysql_num_rows(mysql_query("SELECT poster_id FROM phpbb_posts WHERE poster_id = ‘".$resSess['session_user_id']."’"));

//Setup the multiplier of posts with Mb.
$mult = $numPosts*2*1024*1024;
$limit = $limit + $mult;

//$lim = ($limit/1024/1024);

//echo round($lim,3)."Mb";
//exit;

$goBACK = "<a href=’index.php’ style=’font-weight:bold; font-size:12px;’>Go Back</a>";
}
if(!$res['username'] || $res['username'] == "Anonymous"){
$limit = $max_guest_download*1024*1024;
$selRemain = mysql_query("SELECT SUM(size) AS totalDownload FROM downloads WHERE ip = ‘".$ip."’ AND user_id = ‘0′ AND date >= ‘".$oneMonthAgo."’");
$resRemain = mysql_fetch_array($selRemain);

$totalDownload = $resRemain['totalDownload'];
$userID = "0";
$type = "GUEST";
$goBACK = "<a href=’../forums’ style=’font-weight:bold; font-size:15px;’>Register to our forums now</a> and get ".$max_regis_download." Mb of FREE downloads every ".$timeLimitation." day(s)";

30,000 Mb And Unlimited Bandwidth Only $3.75/mo.