Problems change url

Hello everybody, I hope you have some patience to help me [:)]

The case is to install a wp in a free host, so the url was midominio.site50.com as the site has a lot of users and has become “famous” buy a dominio.com. Now I have the redirect urls, osea when someone enters the url it redirects to this midominio.com midominio.site50.com. Now I want to move everything to midominio.com. I exported the data wp in a folder on my pc. Now I wanted to install one in the wp. Com good then import the data and giving it all I have already saved, but when you install it, and I redirected me midominio.com directory andalusia andalusia old, and if I go to the provider domain, and quito redirection andalusia andalusia enter new domain says “Domain registered”

A little help for a noob [:)]

Thanks in advance