How to Delete the “Uncategorized” Category from WordPress
Step 1) Log in to the WordPress Dashboard.
Step 2) Create at least one new category.
Step 3) Change the default post category to something other than Uncategorized.
Step 4) Click Posts in the left hand menu
Step 4) Click Categories in the left hand menu
Step 5) Hover over the Uncategorized row to reveal the option to delete and click it.