GNU/Linux Elementary OS Updating System Guide
The tutorial shows you step-by-step How to Update Packages & System on Elementary OS LTS GNU/Linux desktop – Step by step Tutorial.
And here I explain How to Update/Upgrade Linux Elementary OS easily on Command Line.
You may also be interested in learning How to Update/Upgrade Kernel.
Especially relevant: after if the suited result is Not achieved, you may be also interested about How to Upgrade Kernel on Elementary OS.

1. Terminal QuickStart
How to QuickStart with Command Line on Elementary OS:
First Update the Apt Repo Sources with:
sudo apt update
Contents