You can't. Splashtop Center can have only one Admin user, and he/she has complete authority to perform all operations in Splashtop Center. Once you have created one or more regular users, you can assign a different user to be the Admin user, if desired. If there already is an Admin user specified, Splashtop Center will ask you if you want to switch to the new user (removing Admin user rights from the current one and giving them to the new one).