activeadmin: adding delete for a nested resource

I have a infrastructure object composed for many datacenters. In the apps/admin/infrastructures.rb I have the following code:

form do |f|
  f.inputs "Infrastructure details" do
    f.input :name

    f.has_many :datacenters do |datacenter_form|
      datacenter_form.input :name        
    end
  end
  f.buttons
end

I can add datacenters with no problems but I don't know how I can delete it from infrastructure form.