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 22.04 "Jammy Jellyfish" from Ubuntu 20.04 "Focal Fossa" can be helpful. 3rd-party repos are handled with a find command.
Some Intel NUC10/11 with I225-LM or I225-V Ethernet chip may cause "freezing" of the OS after this update, if wired Ethernet is in use. There is no known fix; a workaround is to use a USB 3.0 to Ethernet dongle instead.