[How can I update MySQL this way?]

Hi, 

I have been working with MySQL for some time only to require info and make new data. 
But I'm stuck when it comes to update the database. 

Here is the php coding I use to send data to MySQL : 

if(isset($_GET['name']) && isset($_GET['score'])){

$name = strip_tags(mysql_real_escape_string($_GET['name']));
$score = strip_tags(mysql_real_escape_string($_GET['score']));
$sql = mysql_query("INSERT INTO `$db`.`scores` (`id`,`name`,`score`) VALUES ('','$name','$score');");

With the Ajax, we can call an URL like "....?name=NAME_HERE&score=1337" and then make a new line in the Database. This would result into matching a score to a name. 

My question is, how to edit/update a particular item. For example if I use this method to make a profile and the player wants to change a line of it... 

The index of my database is "id" which is auto_increment. I'm not sure if it helps or not.

I have been watching dozens of tutorials but nothing is working for me. If you have any idea how this would be working I thank you in advance.