In order to update the firmware inside the NLi motor you have to stop the EtherCAT communication board.
This can be done writing on 0x605C register (Disable Operation Option Code) the value 0x111.
After that, you can proceed with normal firmware update using NiLAB Starter: https://www.nilab.at/dokuwiki/doku.php?id=integrated_drive_motors:fw_update|