To delete a tracked item, first, tap the meal period you need to modify. Then, find the item you need to remove. You can either tap the check mark next to item to remove it, or you can swipe the item to the left to populate the "Untrack" option. Simply tap "Untrack", and you're all set!
If you need to do this for another day, just tap on the calendar first and choose the day that needs to be altered, then follow the same directions.