If the theme is widget-enabled, you should be able to just wipe the contents there by changing your widgets; just add one.
If the theme is, as I suspect, not widget enabled, you won’t be able to do this without the CSS upgrade and a solid knowledge of CSS. And if you do, there’s still a chance you’ll wipe out the other links, to archive, etc.
Raincoaster didn’t notice you’re referring to the Depo Masthead theme, and thought you’re talking about the sidebar items (where the RSS usually shows up IF you add that widget). In Depo the RSS is a built-in feature that shows up among the header page tabs.