Can't Access Hosting? / How to forward domain?

[#1]

I have a hosting with plusnet (force9) and all my computer systems are run through plusnet.
I have had a website for roughly 10 years, but hired a guy to change it for me. But he can't access the FTP account from his machine?
I called plusnet, but they said he would have to do it through a plusnet internet connection. But I don't have that. So they said try domain forwarding?
How can we launch the website from my domain name I have with plusnet?
Hope someone can help.

[#2]

Unless you have a subscription account I'm pretty sure you need to be on our network in order to access your FTP space. Do you know whether or not the hosting is on a free or paid account?
I don't think you're talking about our CGI servers but if you are then you'll *only* be able to FTP from our network.
If you're going to require that a non-plusnet customer has regular access to your FTP account, then you might be better off hosting your domain elsewhere?

[#3]

I am going to host it elsewhere as I have to buy a plusnet internet line to update the site.
So how do I forward the domain to my new hosting space? Just like domain forwarding www.myplusnetdomain.com "pointing to" www.mynewhosting.com
I hope someone can help.