Via the second admin account called reseller
Having reseller as the creator shouldn't be a problem.
Also, deleting the admin user is allowed, it's not a manditory account.
If you want to change the creator of an Admin account anyway, edit:
/usr/local/directadmin/data/users/adminname/user.conf
change:
creator=reseller
to:
creator=root
only do this for Admin level accounts though.