you need to download win 10 from here: https://www.microsoft.com/en-us/software-download/windows10/
create installer on another pc and change boot order in laptop to match USB or DVD
dell factory reset needs windows running first, kind of silly. the only real option is a fresh install from where you are or we can try a reset
boot from installer
on page after language choices, select repair this pc, not install
select reset, two choices - keep files and settings or wipe it all. I suggest 1st
since you on laptop, there could be a factory reset option as well. It will put win 8 on though