Replacing text of a field with javascript Function

I have a form where I dynamically display checkboxes from an oracle database. But I want to change the checkboxes. This is the text of the form:

<form  id = "Options"> 
                     <?php
                    $conn = oci_connect('DBadmin', 'dbadmin', 'PETLOVERSDB');
                    if (!$conn) {
                        $e = oci_error();
                        trigger_error(htmlentities($e['message'], ENT_QUOTES), E_USER_ERROR);
                    } 
                                $query= 'select * from pettype order by PET_TYPE_CODE';
                                $stmt = oci_parse($conn, $query);
                                oci_execute($stmt); 


                                    while($row=oci_fetch_assoc($stmt)) {                
                                         echo "<label>{$row['PET_TYPE_NAME']}</label><input  type = 'checkbox'  name = 'radio' id = '{$row['PET_TYPE_CODE']}'  value = '{$row['PET_TYPE_NAME']}'/><br /> "  ;        
                                    }                

                     ?>   
                    </form>

And I also created a function that I call when I press a button:

<script type="text/javascript"> 
    function update(){  
            var e = document.getElementById("consultFacts");
            var str = e.options[e.selectedIndex].text;
            alert(str);  
            var elem = document.getElementById("Options");
            elem.value = "My default value";

    }
  </script>   

I have tried the getElementById as I've read but I don't seem to get any changes in the form. And it does enter the function because it does alert(str). Any suggestions?