Upgrading minor versions QT seems to be a hassle, as each version blocks the previous and because of inter-dependencies, Gentoo can’t understand by itself how to solve them. The solution is to tell it to specifically upgrade all installed modules.
sudo emerge -avu1 $(qlist -IvC /qt- | grep 4. | sed s/-4.*//)
This will allow Gentoo to solve the dependencies by uninstalling the old versions, unlike if you only try to upgrade a single package like