Forcing a fresh start with Postgres after updating major version

On my Manjaro machine, I updated packages, and Postgres got updated to version 13.2-1.

Before the update, I had some databases on the previous version. Now Postgres won’t start because it recognises that the existing databases are from the old version. When I attempt to start Postgres, I get:

~|⇒ sudo systemctl status postgresql ● postgresql.service - PostgreSQL database server      Loaded: loaded (/usr/lib/systemd/system/postgresql.service; disabled; vendor preset: disabled)      Active: failed (Result: exit-code) since Fri 2021-03-12 21:30:02 GMT; 2min 53s ago     Process: 3173 ExecStartPre=/usr/bin/postgresql-check-db-dir $  {PGROOT}/data (code=exited, status=1/FAILURE)  Mar 12 21:30:01 xps systemd[1]: Starting PostgreSQL database server... Mar 12 21:30:02 xps postgres[3173]: An old version of the database format was found. Mar 12 21:30:02 xps postgres[3173]: See https://wiki.archlinux.org/index.php/PostgreSQL#Upgrading_PostgreSQL Mar 12 21:30:02 xps systemd[1]: postgresql.service: Control process exited, code=exited, status=1/FAILURE Mar 12 21:30:02 xps systemd[1]: postgresql.service: Failed with result 'exit-code'. Mar 12 21:30:02 xps systemd[1]: Failed to start PostgreSQL database server. 

Those databases weren’t important. They were for my personal pet projects and I’m happy to delete them.

How do I do that? Postgres won’t start, so I can’t delete them through psql. How can I force the latest version to start afresh? Ignore or delete the existing databases.