First, make sure the sensor is plugged into the power source.
For the cloud portal enabled models, it's purely a matter of clicking on the lightning bolt icon. The sensor performed its update within 30 seconds
For Model D and F follow these simple steps:
 - Connect your sensor to a power source
 
 - Download the firmware from the "Firmware" section above
 
 - On the sensor, access the menu by pressing the black rotary switch and select the "Firmware update" option
 
 - From a computer with a Wi-Fi connection, select the "CO2 Sensor" Wi-Fi network. (you will lose internet access, but it will return once the firmware update is complete).
 
 - From your internet browser, go to http://1.1.1.1
 
 - Click on the "Update" button
 
 - Click the "Choose File" button and select the file you downloaded in step 2
 
 - Click on the "Update" button
 
 - The firmware process takes approximately 30 seconds and once complete, you will receive an "Update Successful" message and your sensor will reboot with the new firmware.