[Volundr]

It's not client side, it's server side. The binary format between Postgres major versions is generally not compatible so you need to do a pg_dump from the old database and do a pg_restore into the new one. pg_upgrade [1] can let you bypass this by migrating the binary data directly, but still requires having both the new and old postgres versions installed. There's also things you can do with replication, but since we're talking simplicity I don't think that really applies.

Personally I think upgrades are the one thing MySQL has on Postgres at this point.

[1] https://www.postgresql.org/docs/current/pgupgrade.html