Click on "Posts".
From the drop-down menu "All Categories", select the category the posts are under. Click "Filter".
From the "Bulk Actions" drop-down menu, select "Edit". Click "Apply".
In the "Categories" box, uncheck the category you want to remove the posts from and check the category you want the posts to be moved to. Click "Update."
Bonus tip: If you need to see many posts on your screen, click on "Screen Options" at the top right of your screen, and for "Number of items per page" select a big number. For example, 200.
Article ID: 210
Category: Customize and promote your site