You can turn on the unit on and press the "X" key, this will take you to the main menu. On the right side of the screen it will display X-rite 5XX.
The second way, if the unit will not power on is to get the serial number of the unit, which is located on the unit near the hing, by the power saver button. Once you have the serial number you can call 888-826-3059 and ask which unit you have.
Here is a link to the 500 matrix showing what functions your model has, click Here