Note: Please note that only Premium members can change between Meal Plans/Diets. Free users are offered the Standard/Classic Diet. When you start using the app, the Classic/Standard Diet is activated by default.

When you have chosen a Diet:
Tap on the PLANS tab in the tab bar at the bottom of the screen and choose between the different Meal Plans/Diets.

That means: If you have chosen a Diet and would like to change either the Diet or the Diet settings or change to a Meal Plan just go to the PLANS section again and choose the next Meal Plan/Diet.

If you have chosen a Meal Plan:
To change to another Meal Plan or Diet, please go to the PLANS section and then click on the menu top right hand and then on Change Plan.

This means that you cannot "delete" a Diet or Meal Plan - but if you ever leave the Classic Diet and choose another Diet or Meal Plan you can always go back to how you started off by choosing the Classic plan again.