But the pureos version stays on pureos 8 green. So my packages are outdated (just noticed purebrowsers is on the version 68 of firefox, which is quite old). I have no idea how to update except for the commands above, and I would prefer to avoid a complete reinstall.
deb https://repo.puri.sm/pureos green main
deb http://deb.debian.org/debian buster main contrib non-free
Uh, oh, you are running franken-debian – mixing the PureOS and Debian repositories.
The easiest way out of this is complete reinstall.
Even so, as Amosbatto said, firefox in PureOS amber is not the newest; it is version 68.12.0esr. So might not be worth the effort.
As to how upgrade from green to amber, this requires manually editing /etc/apt/sources.list and replacing all references to “green” with “amber”. I’m not aware of any GUI tool that would allow upgrading to a newer OS release.
How to go back to PureOS from the mix of debian and PureOS you are running – you might want to check that post of mine
Purebrowser isn’t maintained anymore. If the stock firefox in your debian version is not recent enough, another way to get a recent firefox is to use the org.mozilla.firefox flatpak. This avoids Franken-debian.