Changing the Author on a Blog/Post Page
1.) Go to Posts -> All Posts
Select Posts from the left hand menu of your Dashboard.
2.) Find the Post you want to change.
Use the Search Box in top left of the list to find the Post.
3.) Mouse over the Post Name and Select -> Quick Edit
This will bring up a settings menu where you can change various information about the Post.
4.) Change the Author.
Select the Account that you would like to show as the Author of this Post.