This is easiest with GUI access, you can also click the icon at the top right corner of your top bar. Depending on which version of desktop you are running, click either the Settings icon or the “System Settings” option in the menu. Click the “Details” option in the left sidebar or click the “Details” icon under System.

You can also open up Terminal and type:
lsb_release -a

If you are using a non-LTS (Long Term Support) version, you can upgrade any time. If you are using a LTS version, you have to wait until the next LTS release unless you change file located in “/etc/update-manager/release-upgrades” to allow non-LTS upgrades.

If you can upgrade, go back to your terminal and type:
update-manager -c
This will invoke the GUI software upgrade application. Follow the wizard and more than likely, reboot when done.

You can accomplish much of the same task without a GUI using Update Manager, which doesn’t come installed by default.

In your SSH Terminal, type:
sudo apt install update-manager-core update-manager

Then check for upgrades:
do-release-upgrade -c

After you see the message about an upgrade being possible, run:
sudo do-release-upgrade