To delete an ingredient line, simply click on the row selector (the scale icon) and press the Delete key. (To reorder ingredient lines, you click on an ingredient line and click the arrow button on the screen up or down.)
To add new nutritional items, go to the Nutrients view and click "New". You can define all the values for the nutrition from the label itself. (You're not limited to tablespoons or teaspoons.) You should be able to say that in one serving, there is, say, 1 cup, and that in this serving amount (whatever it is), there are X grams of protein, fat, etc.