The only way to install another OS on a windows computer is to flash it to a USB drive using a tool like rufus and then rebooting the computer with the usb drive plugged in. There are probably some obstacles in place, if your computer does not boot into the installer you’ll need to go into the BIOS (usually spamming del or esc while the computer is booting) and change the boot order (make sure usb drive is at the top) and possibly disable secure boot.

If you replace windows with linux you will lose all your files. I’d recommend you first try Linux in a virtual machine, though this might not be an option with your limited RAM. If you’re new to Linux I’d also recommend starting with a different distro that has a larger community so you can easily get answers when you run into problems. I started with Ubuntu, its not the greatest distro and I jumped ship as soon as I was able, but it has dedicated community forums full of all the answers you’ll ever need.