password and admin profile

My site is mvpractices.com. I changed my password but I am able to access the site with new password and the old password. I unable to delete the former admin profile. When I tried to delete the person who had the old admin profile I was unable to do so. I got an error message that said unable to delete because it was a network administrator. The user name for that person was admin. I creeated another administrator and logged in with the new password but was still unable to delete the old admin. I want to delete the admin user name because of the ability to hack the site.

Thanks