Since you didn’t specify which version of OS you have, I assume you have OS 3.0 — if you have OS 2.3, the update is done in a different way (through USB port). Next, assuming yo have OS 3.0, please note that firmware update on OS 3.0 can only be performed in WiFi mode, it cannot be performed when wired Ethernet module is plugged in. This is explained in the update instructions:
https://openthings.freshdesk.com/support/solutions/articles/5000832310-opensprinkler-3-x-firmware-update-guide