I just sold a WP web site. I (Mark) am the administrator with a level 10. The new owner needs to be a level 10 admin now. But if I simply give him my admin account and have him change the nickname to his name, all the posts I had previously created under Mark will now change to his name. That's not what we want. My old posts need to be under Mark and his new ones need to be under his name. He also needs full level 10 access to be able to everything, including deleting any of my old posts if he desires.
I added him as a new user but could only get him up to Level 9. I need him at the highest level, 10.
How can I get the new user to Level 10, while keeping my old account (Mark), but demoting myself to a lower level?