Hallo michaa7,
"apt upgrade" equals "apt-get upgrade --with-new-pkgs".
With both commands you won't accidentally remove packages, though you still need full-upgrade or dist-upgrade to solve conflicts that require removal of packages.
Let me rephrase it: Upgrade may seem save, but without full-upgrade or dist-upgrade you will miss all updates that use "conflict" to replace unwanted old packages. If you continuously use "upgrade" then the number of missed updates will increase over time until the system breaks.
greetings
musca