Cancel the Magix/Xara web hosting as you are moving to a different web host? In the case of 1 see section 12 here
or
You want to use a different domain name leaving the current site where it is?
Assuming you are paying for hosting which includes 1 domain name, and you have purchased another domain name, then the new name needs assigning to the same server locations - how you do this depends on who you purchased the domain name from.
If it was through Magix/Xara then you should be able to do this in the Magix/Xara web hosting control panel control panel. You should also un-assign the current name if possible - if it is part of your hosting package then I do not think you can cancel just the domain name.
If a third party domain name service you need to ask them.