Only system changes have been made to the iRelay classic firmware. iRelay Light now has the ability to DIY & make and convert to a temperature controller. In the management menu it is possible to switch on / off a special relay switch for heating and a special relay switch for cooling. To upgrade to a controller you need a relay module like this one. The default state is off. Only system changes were made on the thermometer. Firmware site
The new upgrade allows you to convert a classic OLED thermometer into a WiFi temperature controller like the V4. In particular, you can control the heating and cooling relay. The initial state of these relays is switched off. To upgrade to a controller you need a relay module like this one.