ok first things first: DON'T ADD THEM AS THE ROOT ADMIN! make them a secondary admin.
ACP -> Users & Groups -> Manage User Groups -> Add a new member group -> base the new group on thew Admins -> click "Setup new group" -> edit the global, Global Permissions, and posting permissions to your needs -> then at the bottom "Moderation Permissions" change that all to yes. Save and add new group. Remember to change "New Group" to Admins with an "s".
-- NOW go do this --
ACP -> Users & Groups -> Find/Edit/Suspend User -> type in the member name in the first textbox "Member Quick Search" and press "Find member" -> click "Edit Details" -> find "Member Group" dropdown box -> Switch them to the Admins profile. your done.
