There is no easy way in 1.8.4
In 1.9 there is a highly experimental rename user feature, that performs a lot of SQL updates, but I really doubt it covers all situations.
I also believe that the admin account is hardcoded in various places like the installer. So renaming it will not be possible. In TikiPro you can setup your admin user to be anything and as all content is linked by Id rather than name it makes changing usernames much easier. something for us to look at maybe in the future.
Much easier is to create a group called Site Admins and give the group tiki_p_admin, then put loobian in that group.