The second tree was created in Family Tree Builder, so you won't be able to edit it online. You must edit the tree in Family Tree Builder and delete this person in your tree. Then save and publish the tree again to your site for the change to take place.
We can unlock your website, so that you can downsize your family tree and preserve it for free. On your family site you can change the settings so that other site members are prevented from adding content to your tree.Maybe you'll find that useful.
I will send you an email with further details to downsize your tree.