How to delete a dashboard
You can delete a dashboard to permanently remove it from Apex.
If you have authorization to delete dashboards, you can delete site dashboards and your own user dashboards. Deleting a user dashboard removes it from your user, while deleting a site dashboard removes it from all users.
Note: System dashboards cannot be deleted.
1. In the web interface, click Configuration > Dashboard Library.
2. Select a dashboard from User Dashboards by clicking it.
3. Click the garbage can icon .
4. Confirm the deletion by clicking Yes.
 
You successfully deleted the dashboard, and it was permanently removed from Apex. If you deleted a site dashboard, no users will be able to view that dashboard.