Upgrading Debian distribution

Hello.

I would like to confirm what i should do to upgrade my Debian from Debian 9 (Stretch) to Debian 11 (bulleyes). The official guide does not mention, explaining with details, how to do a few things i want to do, like installing it from network.

Somewhere in the Debian pages, a forum is mentioned. I searched the upgrade instructions there, and found a promising result:

https://forums.debian.net/viewtopic....PGRADE#p741091

The first answer, by daftranti, starts by changing the apt sources.list file. It suggests these 4 lines:

Code:deb http://deb.debian.org/debian bullseye main contrib non-free
deb http://deb.debian.org/debian-security/ bullseye-security main contrib non-free
deb http://deb.debian.org/debian bullseye-updates main contrib non-free
deb http://deb.debian.org/debian bullseye-backports main contrib non-freeMy sources.list is:

Code:deb http://deb.debian.org/debian/ stretch multiverse main universe
deb-src http://deb.debian.org/debian/ stretch main

deb http://security.debian.org/ stretch/updates main
deb-src http://security.debian.org/ stretch/updates main

deb http://deb.debian.org/debian/ stretch-updates main
deb-src http://deb.debian.org/debian/ stretch-updates mainThe last arguments are different on each line, and i have deb-src lines too. So, the general answer, for what i should do, is to replace all "stretch" by "bulleyes" in the file? Keeping the rest unchanged?

Another question: doing an 'apt update' before 'apt upgrade' is allowed/possible?

One more: what is the difference of 'apt upgrade' and 'apt full-upgrade'? Can i do just the latter one?

The 'apt autoremove' seems clear.

Please, explain everything you answer. Thank you in advance.