Changing the author of a post
We are happy to announce that as an admin of your blog you can now change the ownership of a published post or draft and assign it to anyone who has writing privileges, i.e. Admins (site owner and site contributors) or Writers on your blog.

Here's how to do it:
Head o the Post Settings panel (on a published post or on a draft)
Select who you want to re-assign the post to from the Author drop-down menu
Click on Done
Publish the post
Enjoy! :)