Upgrading from V11 to V12 on Debian install

I have several machines that have version 11 instances on them. These are
all Debian or Ubuntu machines. All of them are pointed to the Postgres
repositories fro the Postgres binaries

deb http://apt.postgresql.org/pub/repos/apt/ buster-pgdg main

dpkg -l shows:

ii postgresql-11 11.6-1.pgdg100+1
ii postgresql-12 12.1-1.pgdg100+1
ii postgresql-client-11 11.6-1.pgdg100+1
ii postgresql-client-12 12.1-1.pgdg100+1
ii postgresql-client-common 210.pgdg100+1
ii postgresql-common 210.pgdg100+1
ii postgresql-contrib 12+210.pgdg100+1
ii postgresql-server-dev-11 11.6-1.pgdg100+1

Googling around, I found this link:

https://scottlinux.com/2015/11/14/upgrade-postgresql-on-debian-jessie-with-pg_upgradecluster/

I plan on upgrading one of the test instances right away. Is the
information in this link the best way to do this in a Debian environment? I
did look at the pg_upgrade documentation, and it looks like I could really
make a mess if I misunderstand even one step.

"They that would give up essential liberty for temporary safety deserve
neither liberty nor safety."
-- Benjamin Franklin