In Debian based distros apt update
updates the list of software versions available from the repository whilst apt upgrade
installs the new versions. There's no confusion here if explained in context. I often use "release upgrade" to characterize the move from one Ubuntu release to the next in order to avoid the confusion some users have when presented with some answer/solution involving the arguably misleading dist-upgrade
(the new recommended full-upgrade
doesn't trigger the same problems).
The update/upgrade duality is problematic only when translating to other languages that don't make the distinction (Spanish, Portuguese, French, Italian, etc.). Likewise, in those languages it's very hard to distinguish between "ape" and "monkey" as their native equivalents are synonymous at a non-scientific level. Reason why I usually describe myself as an "European born African monkey" and many people take an issue why it. The same people usually accept "African ape" without further considerations. I don't care, I'm proud of my monkeyness.
In conclusion, I see no problem with the correct usage of update and upgrade in context and when English is the language used to communicate. And considering the commands don't change depending on the system's language its usage should be exactly the same in other languages but an explanation about the nuances may be required.
sudo apt autoremove
whenever needed. Expanding/boot
just delays the inevitable.