Tap on the PROGRAMS tab in the tab bar at the bottom of the screen and choose between the different Plans. If you have chosen a Program and would like to change either the Program or the Program settings just go to the PROGRAMS tab again and choose the next Meal Plan/Program.
How can I just remove the plan I am on? 
You cannot "delete" or remove a Program or Meal Plan - if you want to go back to the standard version of the app you will have to go to the Programs tab and select Lifesum Standard
Note: Only Premium members can change between Meal Plans & Programs. Free users are offered the Lifesum Standard Program, which is activated by default when you start using the app.