After doing away with the existing disk layout and contents, one basically starts over with an entirely new disk layout and Windows installation into which nothing from a preceding install can ...

The actual upgrading part isn't included in the document, but it will presumably be done through official methods such as Windows Update in Settings, the Installation Assistant, installation media ...

Even if your PC doesn't have the minimum specs, you can still go ahead and install Windows 11. However, with the risk of damaging your device by running Windows 11, is there much point?