You can change a page into post or post into a page by copying the content of the page/post and after that delete the page/post permanently and then a create a new post/page with same content and URI,that’s what the easiest way seems to convert a page into a post and a page into post,and the best and easiest method is shared below:
To Change a Page into Post
1.Open your WordPress Database and run the below query(to open your database if you are using cPanel open the phpMyAdmin and use the SQL tab to run the query)
SELECT * FROM `wp_posts` WHERE `post_type`="page"
2.Now you will see some tables which is list of all the Pages of your WordPress blog,find the page which you wish to convert(you may use the post_title column to find out the page).
3.Now find the “post_type” column for that page and change the value for that page in the “post_type” it will be “Page” change it to “post”.
You are done.
Changing a Post into Page: Follow the same steps just change the page to post in the query(first step) and the value post to page in third step.