pantsonhead

Currently WordPress does not provide the ability to change the post that an item in the Media Library is attached to after it has been set. This plugin allows editors to change the parent post to another post.

Change Media Parent

Allows editors to change the parent post of an attachment after it has been set.

alekc

Sometimes you don’t want to show parent directories in permalink because they are not really necessary or because you know that in the future your child directory will change it’s parent.
For example: 
+Work in progress 
–Site 1 
–Site 2 
+Work Finished 
–Site 3
In this case Site 3 originally have been part of “Work in progress”, and on job done it has been moved under “Work Finished”.
So if you install this plugin your link will be transformed in this way:
domain.com/parent_category/child_directory/post_name => domain.com/child_directory/post_name 
domain.com/category/parent_category => domain.com/parent_category 
domain.com/category/parent_category/child_directory => domain.com/parent_category/child_directory

Remove Parents

Remove Parents is a tiny plugin which remove "category" and parent categories from permalink.

Change Media Parent vs Remove Parents