I tried to change the slug of a category to “personal” in wordpress and got the wordpress message saying “Category not updated“.
It is due to the category slugs can not be the same as tag slugs in the wp-terms table. In order to resolve it you need to perform these steps:
1) Login into wordpress admin area.
2) Click Tags tab. Search for the tag slugs and delete it from the tags.
3) Now, Go back to categories and change the category slug to which you want.