How Can I Install Ubuntu Server on a RPi400?

all those tutorials are correct. and when you say start from scratch to you mean you've dones stuff already on the preinstalled os?

to get Ubuntu onto the pi you need to take the SD card out, plug it into your computer with the [raspberry pi imager](https://www.raspberrypi.com/software/ ) and select the correct options. it will then install Ubuntu for you but unfortunately yes this will clear the current os and any progress you've made on it

np

wait before you do

when you plug the SD card into your computer you can copy those documents onto your computer and you have a chance of being able to then put them onto Ubuntu so you don't lose them.. that is if they are in the correct format which I assume they are