I, ve found the solution to my problem.
here it is...
<?php
$newtest = str_replace("'","’",$_POST[kortenaam]);
$conn=odbc_connect('starmakertest2','','');
if (!$conn)
{exit("Connection Failed: " . $conn);}
$sql="UPDATE starmaker1test SET ID = '$newtest' WHERE Id1 = $_POST[idnummer]";
$rs=odbc_exec($conn,$sql);
if (!$rs)
{exit("Error in SQL");}
echo "$_POST[kortenaam]";
?>
This strips the $string from its qoute and replaces it with it's html entity. Maybe a "russian" solution but it works