To remove all meal plans, navigate to Meal Planner via the main (left) navigation menu.
Then, on the Calendar tab, scroll down to the bottom of the screen, and select Delete All Planned Meals.
To remove a meal plan from certain days individually, navigate to each date in My Daily Log where you have planned meals added (or greyed out/queued up) in the log.
Scroll down to the bottom of the page, and select the Delete button. This will clear all foods (both planned and already eaten) from the selected day.