There is a very well written document on your site:
ubuntu-upgrade-to-24-04-noble-numbat-a-step-by-step-howto-guide#more-20392
The only problem is that 24.04 won’t be out until April 25th, 2024 and it’s Jan 13th 2024.
Hello. 
As detailed here, Ubuntu 24.04’s stable release is indeed scheduled for 2024-04-25. However, you can still install its testing (i.e. development or pre-release) release, which at this point (2024-01-15) is already available (I am typing this text from the testing release of XUbuntu 24.04 “Noble Numbat”).
If you take a closer look at the article’s Step 7, it mentions that if sudo do-release-upgrade returns no release number, then the stable release of Ubuntu version 24.04 isn’t available yet but you can still add the -d option/switch (i.e. sudo do-release-upgrade -d) in order to upgrade to a version that hasn’t been officially released yet, i.e. it allows you to access and install the development version or a pre-release of the software. This can be useful for testing new features in advance, but be aware that pre-release versions may not be as stable as the official releases. 
You can check this option on the command’s manpage (man do-release-upgrade or info do-release-upgrade):
-d, –devel-release
If using the latest supported release, upgrade to the development release
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