You can delete a content class at any time. When you delete a content class, you have the option of reindexing all the namespaces associated with that class. If you choose to do this, the metadata query engine reindexes each of those namespaces starting from the time the namespace was created.
On the Search page, in the list of content classes in the Settings panel, click the delete control () for the content class you want to delete.
In response to the confirming message:
(Optional) To reindex all namespaces associated with the content class you’re deleting, select Reindex all objects in associated namespaces.