You can delete a retention class only if the namespace in which the class is defined is in enterprise mode. You cannot delete a retention class in a namespace that’s in compliance mode.
When you delete a retention class, the retention setting of each object in the class changes to Deletion Prohibited.
In the Retention Classes panel, in the list of retention classes, click the delete control () for the retention class you want to delete.
In response to the confirming message, click Delete Retention Class.