Removing mail hosting

Hi,

I have a free email account and a custom domain but I'm not using it.
I'd like to remove the domain and add a new one.

However, when I try to remove the current domain, I get a message saying "Remove Mail Hosting and proceed for domain deletion". That's cool, but how do I do that?

I poked around in the various account settings and control panel but see no clear way of removing mail hosting.

Thanks.

Stan