Nope you would not lose your posts if you do these steps.
Create a new Administrator account.
Log out of your site and log back in under that new Administrator account.
Delete the WP default “admin” user account.
You will see these prompts when you are deleting the “admin” user account.
What should be done with posts owned by this user?
Delete all posts.
Attribute all posts to:
You would choose the “Attribute all posts to:” Radio button and click on the drop down select option and then click on the new Administrator account you just created. All of your posts will now be attributed to your new Administrator account.