Hey I have to change the value of a hidden form element when a user selects a different radio button. Here is my code:

PHP Code:
<script language='JavaScript'>
function 
UpdateForm() {
window.Signup.encrypted.value 'New_value_here';
}
</script> 
then below is this
PHP Code:
<input type="radio" name="package_type" value="gold" onChange="UpdateForm();">
<
input type="radio" name="package_type" value="silver" onChange="UpdateForm();">
 <
input type="hidden" name="encrypted" value="first_value"
Anyhelp would be great!

It doesnt