How to upgrade to 2.0 ???

[Westcott1]

Is there a guide on how to upgrade to 2.0
"Bare metal" on a RPi4.
Z2m will no longer start,
Using update.sh gives these meaningless (to me!) messages -

npm ERR! code EUSAGE
npm ERR!
npm ERR! The `npm ci` command can only install with an existing package-lock.json or
npm ERR! npm-shrinkwrap.json with lockfileVersion >= 1. Run an install with npm@5 or
npm ERR! later to generate a package-lock.json file, then try again.
npm ERR!
npm ERR! Clean install a project
npm ERR!
npm ERR! Usage:
npm ERR! npm ci
npm ERR!
npm ERR! Options:
npm ERR! [--install-strategy <hoisted|nested|shallow|linked>] [--legacy-bundling]
npm ERR! [--global-style] [--omit <dev|optional|peer> [--omit <dev|optional|peer> ...]]
npm ERR! [--include <prod|dev|optional|peer> [--include <prod|dev|optional|peer> ...]]
npm ERR! [--strict-peer-deps] [--foreground-scripts] [--ignore-scripts] [--no-audit]
npm ERR! [--no-bin-links] [--no-fund] [--dry-run]
npm ERR! [-w|--workspace <workspace-name> [-w|--workspace <workspace-name> ...]]
npm ERR! [-ws|--workspaces] [--include-workspace-root] [--install-links]
npm ERR!
npm ERR! aliases: clean-install, ic, install-clean, isntall-clean
npm ERR!
npm ERR! Run "npm help ci" for more info

-- SOLVED --
RTFM, see post Zigbee2MQTT 2.0.0 breaking changes #24198