How to disable the navigation bar?

In your style.css, take a look at line #138. The selector is h1.category-title. Adjust the padding-top attribute.

Is that space what you’re referring to, or have I misunderstood your request?

Ah, I see what you’re talking about now. First I would check for any settings related to Breadcrumbs in your theme to see if there’s an option to turn them off. If you can’t find any, you can modify line #139 in your style.css file. Add the attribute display: none; to #breadcrumbs.