Changing the Name of the Default Uncategorized Category in WordPress
Go to Posts > Categories and select the category you want to change. Type the changes you want to make in the name. You can clear the 'slug' box and the new slug will be created from the name when you click 'Update'.
Every post created from now on will be automatically filed under your default category with the new category name, until or unless you choose another category.
Default Category in WordPress
Why might you want to change the name? Categories and tags are the two default taxonomies that come with every new WordPress install. In WordPress, your posts must be filed under at least one category.
If you forget to assign a category to your post, then it is automatically filed under your default category. On a new WordPress install, this default category is titled ‘Uncategorized’.
Many writers find it more useful to use a category name that is more meaningful to their readers, and that makes sense if they forget to set a category - or they don't want to bother with selecting one every time they make a post.
If you have more than one category, you can also change the default category for your posts at any time.
Remember, you can assign more than one category to a post, and leaving every post in the default category can be useful if you use a blog page that always shows your latest posts.
Considerations to take into account
If your site has been live for some time search engines may have indexed you site with the old Uncategorized Category URLs and visitors might have bookmarked some of your posts already (lucky you). Those links will no longer work; users and search engines will see a 404 page for the old URL.
This also applies when you change the name of any category.
Any posts already created under the old category name will have a different URL
Redirecting Old Uncategorized URL
You can easily fix that and redirect users to your new category URL or the renamed URL.
This can be done with a plugin such as the Simple 301 Redirects plugin. Once installed and activated, you need to visit Settings > 301 Redirects page and enter your old uncategorized url in the Request field and your new URL into the destination field.
If your old uncategorized URL was like this:
Then you will enter /category/uncategorized/ in the request field.
In the destination field, you need to enter the full new URL including http etc. like this:
Don’t forget to click on the save changes button!