How to update the OS

[ryo]

OK thanks, that's explain a lot for an unexperienced debian old fart like me, but what I mean is, is the result in terms of features the same as reflashing the whole thing? Or is it always advisable to perform a full flash to have the very last version?

That is the beauty of rolling release distributions, you don't need to re-install the OS ever again after installing once (unless of course you fatally bricked the OS, or get yourself a new computer/phone).

I understand the worries if you're coming from Ubuntu or Mint, every OS version upgrade resulted in a broken OS.
Manjaro and Arch don't have this problem.

-Syyu forces a refresh of all sources. it's not the same as dist-upgrade. it's what you do when your local database can't be read due to corruption. it shouldn't be abused, to save hosting resources.

Manjaro/Arch is a rolling release, all packages are always at their latest, there is no multi-release cycle, just a series of packages being updated as they become stable enough to coexist with all other packages at their defaults

I always use -Syyu simply to make very sure that nothing goes wrong, and I'm simply used to it.

There is a little difference between Manjaro and Arch however.
Arch deploys the latest versions of packages as soon as they're available, while Manjaro usually waits a few days to make sure the latest version doesn't break the system.
Like a few years ago a library broke WiFi functionaity in Arch, but those of us using Manjaro didn't have that problem, because the library got patched by the time it reached the Manjaro repositories.
Manjaro updates do break the system occasionally too however, so I'm not saying that Manjaro's testing phase is perfect.