How to upgrade Homebrew PostgreSQL DB

upgrade_pg.sh

# You can see what the old version you have is by looking at
# /usr/local/var/postgres/PG_VERSION

brew services stop postgresql
cp -r /usr/local/var/postgres /usr/local/var/postgres_bak #backup db just in case
mv /usr/local/var/postgres /usr/local/var/postgres<OLD_VERSION> # move it form default location
initdb /usr/local/var/postgres -E utf8 # create new DB in default location
pg_upgrade \ 
    -b /usr/local/Cellar/postgresql/<OLD_VERSION>/bin/ \
    -B /usr/local/Cellar/postgresql/<NEW_VERSION>/bin/ \
    -d /usr/local/var/postgres<OLD_VERSION> \
    -D /usr/local/var/postgres
    
pg_ctl -D /usr/local/var/postgres start # see if it worked