To start, read the official release notes.
If your install fits into "vanilla Ubuntu plus maybe a handful of 3rd-party repos", then this guide for a simple upgrade to Ubuntu 24.04 "Noble Numbat" from Ubuntu 22.04 "Jammy Jellyfish" can be helpful. 3rd-party repos are handled with a find command.
Note upgrade is only supported from Ubuntu 22.04 or later to Ubuntu 24.04. If you are on Ubuntu 20.04, upgrade to Ubuntu 22.04 first. Then once on Ubuntu 22.04, you can upgrade to Ubuntu 24.04.