Initially that product required a data communications unit that plugged into the port on the CPU and converted it to SS232 or RS422. I believe Siemens offered a model with the RS232 or RS422 port built-in so you didn't need the data communications unit.
So, depending on your model, you might need the data communications unit, an RS232/RS422 converter and a 9-pin to 25-pin serial RS 232 cable to connect to the PC running the software and a USB to serial converter.
Presumably you need to extract the program from the unit so you can convert it to something more current, so it might make more sense to try to locate someone local who still has the necessary software, converters and cables to come in and extract the program for you.