In plainer terms, you can update Ubuntu from an older version to a newer one - sure. But if it fails or leaves fog crippled, we don’t just “know” what went wrong. We don’t know how the old OS was setup, what was installed, how it was configured, and so on. It can be troubleshooted but how long that will take or if it’s successful or not, I can’t tell you. The Developers and Moderators and other community members are normally willing to help people - but your pace is limited to their free time.
So… Last night I wrote an article about migrating fog. For this - we know all the steps, and it’s less risky - and you can follow along with it and work at your own pace instead of relying on us.
If you’re strong with Linux and you’re Google-Foo is up to snuff, sure upgrade your OS. If you’re a newbie in a crunch don’t want risks, migrate.