function changefield(checkboxId, elementToChangeId1, elementToChangeId2, checkedCssClassName, uncheckedCssClassName) {

	var selectedElement1 = document.getElementById(elementToChangeId1);
	var selectedElement2 = document.getElementById(elementToChangeId2);
    var checkBox = document.getElementById(checkboxId);

	if(document.contact_form.anonymus.checked) {

		document.contact_form.contact_name.value = '';
		document.contact_form.contact_email.value = '';
		
		document.contact_form.contact_name.disabled = true;
		document.contact_form.contact_email.disabled = true;
		
		selectedElement1.className = uncheckedCssClassName;
		selectedElement2.className = uncheckedCssClassName;
		
	}

	else {
	
		document.contact_form.contact_name.disabled = false;
		document.contact_form.contact_email.disabled = false;
		
		selectedElement1.className = checkedCssClassName;
		selectedElement2.className = checkedCssClassName;
		
	}

}