Before updating from firmware below 1.6.x.0 to current releases, you need to make an intermediate step.
The firmware comes in two parts. 

Firmware Version / Maintenance Version 
e.g. 
1.8.31.0 / 1.8.31.0 

Firmware Update: 
The left side (Firmware Version) is updated via the sysupgrade file. 
This firmware contains the user interface, applications, operating system, SSH, etc. The xxxx_firmware_1.8.31.0.sysupgrade file is used to update the firmware through the 
Upload Firmware menu option. 
Choose the “xxxx.sysupgrade” file and choose upload. Then, follow the instructions. More detailed instructions for are found on the firmware download page for your model. https://www.digital-loggers.com/afwup.html 

Maintenance Update: The Maintenance firmware (.core) contains the hardware control system, LCD, keypad, GPIO, etc. and is updated less frequently than the application/system firmware. 
If the displayed firmware version is a link, e.g. then the maintenance files should be updated. 

To update the maintenance (.core) file, click on the link or from the menu, click on the support link. 
You can also look on the support page to see maintenance file update recommendations. 
Maintenance update complete instructions: https://www.digital-loggers.com/update_core.html 

In the Maintenance section*, choose the file to upload. Uncheck the “Confirm operations from keypad” if you do not wish to confirm the update on the controller itself.  Press the “Start Maintenance” button. 
More complete instructions: https://www.digital-loggers.com/update_core.html 

*If the settings are protected, reset the protection. 
Press the reset button near the RJ-45 Ethernet connector and wait about 5 seconds. 
You will hear a beep and arrive at the reset menu. You can use the Up/Down arrows to select the kind of reset. The default is "Clear Lock Bits: Clear protection bits only", which is what you want. Press the cycle button.

After the update you don't see that the Maintenance Version has changed or the firmware version link remains, logout and login again, try the update again. Then recheck the version. 

After these versions are 1.8.31.0, you can proceed to update to the latest versions.
