It is a straightforward process to adjust each meal so that each nutrient is within your diet goal (the nutrient will be displayed with a green background). However, unless you are on a very strict diet, you don't need to make every meal have every nutrient green. You should focus on weekly averages and adjust meals that will bring your weekly averages into line (see the values at the top of your weekly menu).
If you feel you need to adjust the servings for a meal, you can do one or all of the following:
EditAdding Additional Recipes/Items
(1) Make sure you have everything on your meal that you'll be eating or drinking, such as vegetables, fruit, beverages, desserts, etc. You can add recipes using the +recipes link or items using the +item link (see these at the top of the meal display) to add simple things like milk, fruit, etc.
You can search for and add additional recipes. While searching for recipes, it's best if you have the "Fits My Diet" checkbox ON. This will give you only recipes that won't exceed your diet.
Also note that you can sort the columns for calories, fat, protein and carbohydrates. This makes it easy to find High or Low Fat/Carb/Protein recipes.
EditDeleting Recipes/Items from the Meal
You can delete recipes or items from the meal using the trash can

to the left of the recipe.
EditAdjusting Serving Sizes for Recipes
You can alter HOW MUCH you will be eating of each recipe or item. You adjust recipes servings by clicking on the (x of y) link next to the recipe title. For example, if your meal has
Turkey Bratwurst Sausages (1 of 2) you would click the
1 of 2 link and change the values for how much you'll eat and/or how much you'll prepare.