Here is the perfect steps to change wordpress post author:
1) Login into wordpress admin area.
2) Click on Edit in the Posts section.
3) Select the posts for which you need to edit the author details.
4) From the top there is drop down for bulk actions -> select edit and apply.
5) Now, you can change author, comment, status, pings, sticky, categories etc..,
6) After changing the value of author..click on update posts..