DOS is an older system and may or may not upgrade to Windows 8. Some say you can but most say you can't. You can run it on XP or Windows 7 without much problem but the question is? Why would you want to? I would just forget 8 as it's junk anyway and look up how to run it with 7. Or wait a few months and dump it and upgrade to Windows 10 which is going to be really good.
I do believe you can downgrade but you best to check with the make of your computer. Call the tech support they would be much better to help you.