To update your system you need a network connection, use your VNC connect to get to to the Pi.
On the task bar (at the top) you should see the icon for the terminal window. Open the terminal and type in the following at the prompt:
sudo apt update
? then press the enter key. Make sure it's all lower case. Linux is case sensitive!
After a few minutes, you will receive a response stating x packages can be upgraded.
or All packages are up to date.
If you get the first message, enter the following at the prompt:
sudo apt upgrade -y
?then press the enter key. Make sure it's all lower case.
You may want to reboot your Pi if it hasn't been upgraded in a while.
Do this by typing the following at the prompt:
sudo shutdown -r
? then press the enter key.
type in
exit
? then press the enter key.
That'll bring your Pi up to date after it re-boots. You may have noticed pi2B or pi3B at the prompt. That's your Pi model.
This link can help you if you haven't added JMRI to the main menu
Use this link for installation of JMRI
?To update JMRI, start Decoder Pro, go to Help, check for updates and you'll get information on the latest production and test releases.