When you are interested in finding out, which firmware version is running on your machine prior to updating, you can use the 'M115' command. Please make sure your 3D Printer is connected with your desktop PC (machine control panel).
In this example, Simplify3D is used. Other slicers like; Repetier, Cura, etc. will have a similar feature build in.
In the communication window. After sending this command, your machine will send the firmware name and information.
This information can help you select the correct firmware from the firmware archive solution article.