You can’t replace the Site Title and Site Slogan content areas in the Artful theme with a logo image without digging into the theme file and manually modifying the HTML and CSS code.
If you go to Settings >> General in RapidWeaver, you can add your logo to the Site Logo box that is located on that settings page. The logo is displayed near the upper left corner of the Artful theme though, so it might not be exactly where you want it.
If you are looking for more flexibility on where you can place your custom logo on the page, a Blank theme might work better for you, or a framework like Source or UIKit.