FLM3E broken after firmware upgrade

I tried to update my FLM3E firmware from v368 to v380 using the 'upgrade' button on the website, after which it no longer works: I can't connect through LAN on 192.168.255.1 , power led and heartbeat led are always on. I tried to look for instructions for reflashing but all I can find is related to FLM2. Can anyone advise on how to solve this?