To bulk edit WordPress posts categories, you can follow these steps:

1. Log in to your WordPress admin dashboard.
2. Navigate to the “Posts” section by clicking on “Posts” in the sidebar menu.
3. On the Posts page, you will see a list of all your posts. You can filter the posts by category if needed.
4. Select the posts you want to bulk edit by checking the checkboxes next to each post. You can select multiple posts by holding down the Shift key or the Ctrl/Cmd key while clicking on the posts.
5. Once you have selected the posts, click on the “Bulk Actions” dropdown menu located above the list of posts.
6. From the dropdown menu, select “Edit” and click the “Apply” button next to it.
7. A bulk edit panel will appear with various options. Look for the “Categories” option and click on it to expand it.
8. You can now select the categories you want to assign to the selected posts by checking the checkboxes next to each category.
9. If you want to remove a category from the selected posts, uncheck the checkbox next to that category.
10. After selecting the desired categories, click the “Update” button to save the changes.

WordPress will now update the categories for the selected posts in bulk. Make sure to double-check the changes to ensure they are applied correctly.

Please note that the specific steps or options may vary slightly depending on the version of WordPress or any installed plugins that modify the post editing interface.