Change a post's slug
In some cases, while using pretty permalinks you might want to modify the post’s slug, either because you accidentally used the same title as another post and ended up with a ‘-2’ at the end of the URL or you are using a page and used a slug that triggers a post type archive etc.
To modify the slug of a post, page or custom post type edit the post and click the edit button below the URL
modify the slug and then click OK
finally make sure you update your post.