The account numbers used in the admin fee process are managed in the Fund Class Defaults.  
  1. Fund Class Defaults can be found in File Maintenance > Fund >  Fund Code Maintenance > Fund Class.
  2. Double-click on each class and scroll down one screen and you will see the Admin Fees Offset Account.  
  3. Change that value to the new account for each class affected.
It might also be necessary to change any GL overrides you might have in place for some funds.