The right course of action would be to contact the owner of the site (the guy in France now) and get from him the login details to your hosting account with the hosting company (1&1 Internet AG). If he does not give you the details, you cannot claim access to the site. If you cannot contact him, either try again or contact 1&1 hosting for access to the hosting account with whatever credentials you have.
Sorry, if you cannot do the above, we cannot help. It is NOT a WordPress problem, but something related to ownership and other rights (legal?). I hope you understand.