Confused about user names-owner, administrator

I'm a little confused by the two user names on my computer. Now I'm the only user of this laptop. When I just received the new machine and set up things, I entered a name (call it AA) for registration/owner and maybe other purposes. Later when prompted somewhere I entered another name (call it BB) for administrator.

Now, using the classical XP login screen (the one with a display picture), when the computer is turned on, the name AA is already filled in the user name field, I just enter password. If I replace AA by BB here and type the same password, it worked, too. However I don't know what's the use of the name AA elsewhere. When going to User Account, I only see one name there: the administrator, BB.

(When logging in using the quick login screen, the automatically filled user name is BB, not AA, unlike above).

So my question is, what's the relation between AA and BB? One is owner, one is administrator? I know how to change the name BB, but how can I change the name AA?

 

the Administrator account cant be disabled/removed. While your account may be of group administrator, there is an account with the username administrator as well that is used for non typical situations (for instance...safe mode)

 

Sorry I'm not very clear... In my above example, BB is the administrator, but I'm not sure what AA is and how to change its name (not remove, just change)...?