Mario Peshev

Delete all Custom Field entries assigned to posts that do not exist in the posts table.
Navigate to Settings -> Remove Unused CFs and delete all postmeta for non-existing posts.

DX Remove Unused Custom Fields

Does exactly what it says.
Installed, navigate to the settings page, click "Delete" and Done! Cannot be easier than that.
Thank you!



Simply Awesome!

Delete the Custom Fields from your postmeta table where assigned posts no longer exist.

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 Unused Custom Fields vs Convert Post Types