The history function allows you to access past versions of your plans and to revert to any past material. To access the history function, first click on your lesson menu in the upper right corner of the lesson you want to change. Next, select the lesson history icon and choose the past version of the lesson to which you want to revert. Finally, select the blue, rollback to version # button. You will see the lesson has changed to the past version.
Note: If you erased a lesson and then chose the option to delete the history, you will not see versions of your lesson plan before you took this action.