Your username is set as the blog author by default.
You can change your username in the Account Settings.
Or, you can hide the blog post author displayed inside a blog post. Simply open the blog post you want to edit.
Then, open the post header settings.
And hide it by clicking on the eye icon.
To hide the author for all blog posts, find the blog page/section and open its settings.
Then, go to the Style tab and hide the Author.