There are two ways to delete attachments, managed documents, processes and value streams:
On the summary screen
In the details screen
Delete from the Summary screen
Select all the items you want to delete
Click the Delete button
Enter a reason for deleting the items (attachments will have a confirm deletion message)
The items will be deleted from the list
Delete from within the detail screen
Open the item you want to delete
Click on the Delete button
Enter a reason for deleting the item
The item will be deleted and the page will refresh your dashboard