The admin account is special. I don't think it CAN be deleted. However, ...
If you create another account to be your 'true' administrator account by making it a member of the admins group, you can remove the admins group from the admin account, making it an ordinary user - a member of the Users group. I don't think you can ever make someone NOT a member of the Users group, because it is special as well.
You can't remove Users group but again you could take the approach of creating your own groups with all the rights you want them to have, then place your individual user accounts into your new groups. Then remove all access rights except maybe OpenShared from Users group.
The way Access does this, if a user is member of Users group and XYZ group, that user inherits whatever rights are held by each group combined. So if Users contributes 'nothing' and XYZ holds all the rights, no harm is done and the individual user has XYZ's access permissions. In this scenario, admin (user) is a member of the Users group but inherits nothing from that membership. No power = no threat.
Of course, you do know that you should NEVER EVER IN A BAZILLION YEARS give individual users any rights whatsoever? Of course you knew that, but I'll just remind you. Users should always inherit their rights from groups. Makes management of users so easy. Just create the groups and then as users come in, assign them to the appropriate groups. (If you are from an ORACLE environment, think 'roles' instead of 'groups' and you have the picture.)
You also know, of course, that you must adjust ownership of all objects to not belong to 'admin' but instead to belong to the account you named as the new administrator? I knew you were aware of that, but it is an often-ignored requirement for securing DBs. See, regardless of other permissions, the owner of an object ALWAYS has control over the object. So if someone comes in as admin, even if you tried to make it brain-dead, it won't be so powerless unless it also doesn't OWN anything.
