What I can do to fully upgrade my system?
I don't know which packages are critical for your productivity, so please be careful. What I would do, in tty1 with no xserver running, is this:
# apt-mark showhold
Take all held packages off hold.
apt update
apt full-upgrade
Now look at the packages to be installed, removed, and updated. If you are concerned about a package to be removed, first look in the packages to be installed, and see if a newer replacement is being installed. If you're still concerned, you can use google and the debian package search site to see if you can determine what is going on.
Usually you can do this and end with a "clean" system, and if something important to you was removed, you should be able to reinstall it. I have gone so far as to lose my entire DE, and then replaced all of it by reinstalling the needed packages.
Note -- putting packages on hold is always a dangerous game, and often ends badly.