To edit an Assessment Grade Plan, and remove a Description for grading:

1.) Start from your onRecord persona.
2.) Navigate to Settings > Grading > School Year Setup.
3.) Using the filter on the right, filter for the Assessment Grade Plan you want to edit, then click View.
4.) Click View to the right of the Grade Plan under the appropriate term.
5.) Locate the Description you want to delete, and click the Delete link to the far right.