To begin installing security updates, the first thing is to update your repository index, which would instruct the server to check all lists of packages that are new or out-dated.
Update your repo with the following command:
sudo apt update
Once, you’ve done that, you will need to upgrade them if any new packages are available.
You can either run
sudo apt upgrade or sudo apt dist-upgrade
The difference here is that apt upgrade will automatically install an update without removing any packages while the apt dist-upgrade will update new packages, install new packages as a dependency of the upgraded packages, and remove packages that are broken by upgraded packages.