Step 1: Login to your WordPress website.
Step 2: Click on the posts menu item on the left-hand side of the admin menu.
Step 3: Click on the Categories submenu item.
Step 4: Scroll down until you see “Featured Image”.
Step 5: Click the “add image” button.
Step 6: Either upload or choose an image from your library.
That is it, you are all set 🙂