Click into the recipe you want to modify either directly within plan view screen or within plan's schedule edit screen.
In the recipe details view click "More Options":
Then click "Make a Copy" (or "Make A Copy in Cookbook" if you were within Schedule screen):
From here, you can make changes to your recipes - including removing unhealthy ingredients and substituting them with healthier ones. The best part? You can watch our health rating change in real time as you type in your ingredients!
After you are done with your changes, click on "Save". In the recipe details view that appears after you save, click on "More Options" and then on "Update Copies in Meal Plans":
In the popup put a checkmark next to the plans you want to update and then click on "Update":