Can not edit the index.html site

I designed a Site www.alter-porthhof.de and maked it ready for editing with contribute. Everything works fine, but I seems that I maked one mistake: I edited the index.html on my computer for testing, and than I gave the user domainowner the admin rights. He can edit everything and it works fine except the index.hmtl site.

How can I change this? Is it possible to delete the hole contribute thing, and than to from the beginning?