The company administrator is the only user that may delete this company.  The company administrator may assign the administrator position to another user.  See company setup under user access page.

Level 5 access may do everything the administrator may do except delete the company.

Hint:  You may create duplicate contacts, but you may not create duplicate administrators.  The best way to make sure you access the administrator contact information is to use the company administrator link found under Company Setup Profile.  (Duplicate contacts are never recommended.)