hp]<?php

$result = mysql_query("SELECT password FROM users");

$row = mysql_fetch_array($result);

if(md5($_POST["pass"]) == $row["password"]){

$old = md5($_POST["pass"]); //md5 version

$hash = hash("sha256",$_POST["pass"]); //sha256 version

mysql_query("UPDATE users SET password='$hash' WHERE password='$old'");

}

else{

// you code this part

}

?>