You can do this by opening up the RockMelt menu from the upper left and:
 

• Choosing Options / Preferences
• Going to the "Under the hood" tab
• Under "Privacy," uncheck the option to "Use a prediction service to help complete searches and URLs typed in the address bar"
• Then, on the same Options / Preferences screen, click on "Clear browsing data" button and select option to "Clear browsing history"
• Finally, restart your browser