I want to completely replace Ubuntu with Lubuntu

I accidentally issued some commands I thought were safe in the terminal, and I ended up with no System Settings and lots of other missing functionality, but the OS still boots normally. I've decided I want to install Lubuntu instead of fixing Ubuntu for a fresh start and since my laptop is running on a 1GHz dual core AMD CPU.

I created a bootable USB as I usually do and placed Lubuntu 17.10 amd64 using Rufus 2.14.1086. I have GRUB that was installed with Ubuntu upon first install I still have Win8.1 which I still want to keep.

PS: I also tried creating a startup disk from Ubuntu

The question is: How can I boot from USB with GRUB2 so I can overwrite Ubuntu?

I suggest that you try the Lubuntu 18.04 LTS iso file lubuntu-18.04-desktop-i386.iso, and if it works in your computer, it is a better choice, because it has support for 3 years from now.

Lubuntu 17.10 has support for only 3 more months.

• Backup your personal data (files, that you want to keep) to another drive.

• When you boot from Lubuntu and start the installer, at the partitioning window, you can select Something else and select the partition, where you have Windows to re-use it (and install alongside Windows).

• The installer should install the grub bootloader and find Windows for you automatically. If Windows is hibernated or semi-hibernated (alias fast startup), there are problems, so you should turn that off (in Windows).