The program works only in LiveCD mode. To use the utility OS-Uninstaller, you should boot from the LiveCD=>Install=>Run and use.
sudo add-apt-repository ppa:yannubuntu/boot-repair sudo apt-get update sudo apt-get install -y os-uninstaller && os-uninstaller
Choose the OS you want to remove and click "OK"
A confirmation window will appear, Click "Apply" to start the removal.
Warning: the default settings of the Advanced Options are the recommended ones. Changing them may break your boot. Don't modify them before asking advice.
"Although personally I would not formatted the partition after remove the system. I would be better after the removal format via the program Gparted in my desired format."
When the removal is finished, reboot and check that your system has been removed.