Here's a nice little video on how to figure this out. Note that video features the Empress Reverb, but that the process for figuring out the firmware version on the Echosystem is exactly the same.
But if you don't want to go to Instagram or watch a video, I'll just tell you!
When you turn on your Echosystem, you will see some of the modes lights and presets lights turn on.
The preset light represents the whole number of the firmware version.
For example:
Preset 1 BLUE is 1.00
Preset 5 BLUE is 5.00
Preset 1 GREEN is 6.00
The modes light represents the decimal number of the firmware version.
For example:
Hall BLUE is 0.01
Sparkle BLUE is 0.05
Hall Green is 0.13
Echosystem
Digital BLUE is 0.01
Digital GREEN is 0.13
So if your Echosystem turns on with Preset 2 BLUE and Digital GREEN, the firmware would be 2.13!