Your PhotoSpring device model can be determined by looking at the back of your device for a sticker that contains your device serial number.
If your device doesn't have a sticker, it is a first generation model.
Otherwise, the serial numbers will look like this:
x : is your model number
yyyyyy : is the unique ID of the manufactured device.
So if you see a serial number 012123456 then the first three numbers of 012 mean that you have a model 2 device. A model three device will have a 013 in front, and a model for device will have 014 etc...