[Gary MichaelSupport Manager]

This should help get your started. You just need to modify the {FIELD_ID} text to match the IDs of the respective fields.

add_filter( 'syncs3_put_object_file_path', 'customize_syncs3_path', 10, 6 );
function customize_syncs3_path( $path, $file, $file_name, $field_id, $form_id, $entry ) {
	$fname_field_id = '{FIELD_ID}'; // Change {FIELD_ID} to the ID of your first name field
	$lname_field_id = '{FIELD_ID}'; // Change {FIELD_ID} to the ID of your last name field
	$fname = rgar( $entry, $fname_field_id );
	$lname = rgar( $entry, $lname_field_id );
	$path = "{$fname}-{$lname}-{$entry['id']}"; // Make sure the new path includes the file name
	return $path;
}