You don't have to go out and get any extra programs. You can delete all of your web site files from the File Manager or the Upload Tool. Both are available under the "manage hosting" icon. You can also simply use Internet Explorer in the FTP mode. For an explanation on how to use Internet Explorer, go to my help page on Using FTP help page.
However, it looks like you just started and used the Website Wizard. You only have one page so you probably only have a "index.html" and a "style.css" file. If your going to switch to a different Wizard layout or theme, just ignore the existing files. The Wizard will overwrite them when you publish anyway.
If your planning on using a Template, from the Template Gallery, just upload it and ignore the old files. You can edit the templated from the editors available in the File Manager. The Website Wizard database will never actually go away, but if your working with a Template, you don't need it. I keep a Wizard creation, for test purposes, in the same account as my main site. As long as you stay away from the "publish" button, you don't have anything to worry about. Note that the when you are working with the File Manager, there is no need to "publish".
