You can download it now on the Epic Games Launcher and GitHub. This is a pretty significant release featuring many new features, including modular control rigs, adaptive tessellation for Nanite, a new motion design mode, and much more.
Perhaps more importantly, this also means the new licensing model is now in effect. The new pricing only applies once you upgrade to Unreal Engine 5.4. You can continue using Unreal Engine 5.3 or older under the previous terms, so choose carefully!
If you are upgrading, brew a cup of coffee or tea and check out these resources while you wait: