Follow the link to your particular model (note, don’t update firmware just because you feel good about it, unless you have a specific problem you are trying to fix)
https://watts247.com/manuals/gw/Firmware/
BE SURE YOU HAVE THE CORRECT FIRMWARE FOR THE CORRECT MODEL. WE WILL NOT BE HELD RESPONSIBLE
Here is a video as an EXAMPLE updating the 6000T, the procedure is similar for other models (make sure you have the correct firmware downloaded)
Firmware Update 6000T