In the Profile screen you can set your Daily Calorie Goal. If you have other people added to your plan, they can set their Daily Calorie Goal too.
When setting your calories, you can either use the calorie calculator to help you calculate calories or you can turn off auto calculate calories and choose your own.
When you change your Daily Calorie Goal this will:
Update the target calories from today onwards
Adjust all the recipes you'll see in the Recipes tab to help you hit your goal
Update the meal calories you'll see in the plan creator
It won't update the recipes that are already in your plan.