You can download Galaxy Note 4 stock firmwares on this page. These are 100% stock firmware provided by Samsung Kies and will allow you to fully restore you phone back to 100% stock phone.
OTA updates not working for you? You can also use the unroot method to update your stock firmware to the latest software if OTA updates are failing or if KIES is not working for you. See unroot instructions below and use the appropriate Note 4 stock firmware for your model.