sudo apt-get update -y && sudo apt-get upgrade -y
Then, it's best practice to run
sudo apt-get dist-upgrade -y after.
apt-get update refreshes the package index files from sources listed on
apt-get upgrade will fetch new versions of packages that are installed on your system. This command will fail if there are conflicting packages, hence the need for
apt-get dist-upgrade. The versions it will install depend on the index
apt-get update downloaded, so running
apt-get update beforehand is important.
apt-get dist-upgrade does the same thing as
apt-get upgrade, but handles changing dependencies. It will attempt to upgrade more important packages at the expense of less important ones. Some packages may be automatically removed.
-y switch tells
apt-get to answer yes on any questions it might ask.
&& part tells whatever is running the command to execute the second command if the first is successful. So an
apt-get upgrade won't happen if ever
apt-get update fails.