Can anyone please explain for us that are not so tech-experts
what steps are needed to replace the installed windows with Libreelec
It used to be that you created a bootable USB stick using the Libreelec USB SD Creater tool. On first boot using the created stick it asked you where you wanted to install your Libreelec on your computer. After that it should simply boot to your installed LE system.
How to install LibreELEC on HTPC - A lightweight Kodi operating system
That's how I have always done it in the past, but things might have changed since there is a move towards running off USB/SD recently.