To setup automatic security updates follow the instructions from Ubuntu.
To run security update manually
A full update of all packages can be done using the follow, remember this may create some issues is one update makes something else you have no longer work properly. You should test to make sure things all work after the updates (for production systems obviously you should test things before [first updating the staging server to make sure the updates don’t cause any problems] and after the updates).
First update the local package index (to find what needs to be upgraded).
sudo apt-get update
Then upgrade the software.
sudo apt-get upgrade