

Use the Windows partition manager to shrink the existing Windows partition to the desired size, to make room for Linux.

NB it's important that you be able to fit the media entirely in memory. I recommend the Debian netinst CD, which is about 600 MB. Here's a sketch of what I was able to do to get Debian Bullseye installed on my laptop that shipped with Windows 10. But it's not for the novice and it's not simple. It is possible to install Linux on a Windows 10 UEFI/GPT system without any other media.
