Open the carname1.tab in your hex editor. Go to the view where you see the text, and over-write the name "Sports Sedan" with the name of your car. Be careful not to exceed 23 letters, or the name will get clipped in-game. The information below the name can be entered optionally, as it only shows up in Career mode, and is not seen otherwise. Save the file when you are done.
Once you are done putting a name, you can move ONWARD.