drupal identify which content type is not used
Just go to http://example.com/admin/content as user 1 and filter content by content type. If there is nothing, then content type is not used. Note that there may be views or modules that expect some content types to exist, even if you are not using them at the moment, so always make a backup before dropping them.

For fields, go to http://example.com/admin/reports/fields - you will get a nice list what is used where.