Identify voltage by looking into gang box
Quick answer is that 240v only requires two wires (black and red).  Four wires would be power coming in, and the switched power from the thermostat going out.  If there are 6 wires, then power comes in, and the thermostat controls two pairs, or one pair is power out to another thermostat and one pair out is to a heater.  How the old thermostats were hooked up should tell you that.