Mario Peshev

Delete the posts from Custom Post Types that are no longer active for the install.
Navigate to Settings -> Remove Oldies and delete the posts from a given post type that is not active anymore.

DX Remove Oldies

Delete the posts from Custom Post Types that are no longer active for the install.

Stephanie Leary

This is a utility for converting lots of posts or pages to a custom post type (or vice versa). You can limit the conversion to posts in a single category or children of specific page. You can also assign new taxonomy terms, which will be added to the posts’ existing terms.
This plugin is useful for converting many posts at once. If you’d rather do one at a time, use <a href="https://wordpress.org/extend/plugins/post-type-switcher/" rel="ugc">Post Type Switcher</a> instead.

Convert Post Types

Wordpress 4.9.5

No better plugin for converting categories to custom post types. And vice versa.

Still works great

A bulk conversion utility for post types.

DX Remove Oldies vs Convert Post Types