public function update($notificationLevel) {
        $data = Values::of(array('NotificationLevel' => $notificationLevel, ));

        $payload = $this->version->update(
            'POST',
            $this->uri,
            array(),
            $data
        );

        return new UserChannelInstance(
            $this->version,
            $payload,
            $this->solution['serviceSid'],
            $this->solution['userSid'],
            $this->solution['channelSid']
        );
    }