While the Ubuntu distribution provides long term support for 5 years. They periodically release point upgrades. For example 16.04 has been updated to 16.04.1

sudo apt update

sudo apt full-upgrade

this will upgrade you system and its not a bad idea to reboot the server

sudo apt-get upate

sudo apt-get dist-upgrade

keeping you server updated makes sure that any problems found are fixed

 sudo apt-get upate

sudo apt-get do-release-upgrade

is needed when you are upgrading from say, 14.04 to 16.04 etc