Loaded Ubuntu 18.04 by mistake, followed isntructions, now I cant reboot from usb to install Ubuntu

I loaded Ubuntu 18.04 and ran the instruction steps until removing the kernels, when I tried to install the ppa for the up repositories (sudo add-apt-repository ppa:ubilinux/up), it said there was not release available and I realized that I had installed Ubuntu 18.04. I burned a usb with 16.04 but when I try to boot the machine it goes to safe more because its missing the kernels. I dont know how to fix this.