It sounds like you need to uninstall WordPress. If your web host includes a hosting control panel then you might have an item called “Quick Install” where you can view your current CMS installations. If you see WordPress listed somewhere you should be able to click a red X and remove it.
If none of that helps then I suggest you call your web host and ask them to walk you through uninstalling WordPress to setup a pure HTML site. They should also be able to walk you through setting up an FTP account so you can begin to upload files.