A manual grade item is used for work that occurs outside of Moodle.
NOTE: These steps cannot used to delete activities completed inside of Moodle. To remove Moodle activities like Forums, Quizzes or Assignments you the activity grade type setting to None or delete them from the main course page/weekly view of your course.
Scroll to the top of the main page of your course.
Select the Grades option from the secondary navigation.
Select the Gradebook Setup option from the drop-down menu.
Locate the Manual Grade item you want to remove.
Click the Edit menu for the item
Select Delete.
Confirm your choice.
Click the Continue button.
Repeat as desired.