To delete a recurring panel instance from the project database, go to
Ribbon: DM Electrical->Distribution Equipment-> 
Delete Recurring Panel Instance from Database
Pulldown Menu: DM Electrical->Distribution Equipment->Recurring Panel Instances->Delete from Database
Select a recurring panel instance from the list. You can select multiple items in the list using the SHIFT or CTRL keys. Press the Delete button to delete the selected instances from the database.
Recurring panel instances that have been placed on a drawing will not appear in the dialog box. Removing an instance from a drawing using the standard CAD ERASE command will also remove it from the database.