Remove w10

I am trying to remove w10 and go back to Ubuntu.
I am signed on as Administrator and not as Local Administrator.
Followed the instructions here on how to remove the Fast Start.
However, they are not working.

Any ideas how to do this?
Any help appreciated.

Ummm...... why not just boot from the Ubuntu install USB flash drive or DVD and erase the drive before you install Ubuntu?

The way to bypass Windows 10 fast startup is to hold down shift key when you click on Shutdown. Also the command:
powercfg -h off

will also disable fast startup.