When you sign up for a host you point the dns on the registrar to the host. The host gives you the dns info. That's how people go to your host when they enter your domain.

You don't have to start from scratch. I would remove my files from the old host before leaving. Also, you can just reload them (ftp) from your computer to the new host unless you want to start your site over for some other reason.

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Good Success!
James
Douglas County Master Gardeners
"We don't always get what we want, but we always get what we expect."