Hi,

First you'd have to contact Magix and cancel your domain with them. Please also see the terms of service for the Magix online services/Website Maker. There's a bit about account cancelation in there.

http://www.magix-online.com/uk/terms_of_service.1495.html

An authorization code will be issued and sent to you. You will need this code when you initiate the hosting of that domain through another provider.

I hope this helps!