How to free up space from Debian to install another OS?

Question

linux

I'm on Windows, I need to install Ubuntu, the image of which is already ready on the flash drive... However, the fact is that I already installed Ubuntu - it works. Ubuntu installed completely by itself, I just chose a USB flash drive with it in the BIOS or somewhere else. The problem is different: it so happened that on Debian (the last OS that I installed), I allocated almost all the space, in Ubuntu there is not enough memory. I need to either format all the space occupied by Debian and the failed Ubuntu install, or something similar.
Also:
1) Windows should stay, I would not like to restore it, so the option of formatting the entire hard drive is not suitable.
2) I am an inexperienced PC user, so tell me more, please.

Answer 1

download any section editor, write it to a USB flash drive, boot from it and redistribute the space.
for example https://gparted.org/download.php