I downloaded Mac High Sierra and at the installation process it is blocked I can't even get to the operating system of my Mac mini

on my App Store for updates, there was a message that said I must upgrade to MacOS then I downloaded it, after there was a restart choice I followed it then as it installs from the beginning a pop up screen says "an error occurred while updating firmware. quit the installer to restart your computer and try again" I have been restarting several times and am still stuck can't even access the Mac operating screen to uninstall MacOS...PLEASE HELP