Little Problem

Little Problem

Hi

I am using a sample code found on a website it works fine other than it duplicates entry rather than changing existing post how do i fix it to change rather than add another entry? :
  1.     <html>
          <head>
            <title>Hello world</title>
            <script type="text/javascript" src="jquery-1.9.1.min.js"></script>
            <script type="text/javascript">
              $(document).ready(function(){
                $("#CategoryFrm").submit(function(event) {

                    /* stop form from submitting normally */
                    event.preventDefault();

                    $.post( 'controller.php', $("#CategoryFrm").serialize(),
                      function( data ) {
                          $("#status").append(data);
                      }
                    );
                  });
              });
            </script>
          </head>
          <body>

            <form action="/" method="post" id="CategoryFrm">
              <input type="text" name="category">
              <input type="submit" value="Save">
            </form>
          </body>
        </html>