Move Website to new URL

Ok. I will have to use these name examples so i don’t upset the client.

http://www.website1.com is pointed to the hosting package, website project is done and its working.
Now he wants the main website to be http://www.website.com.. How do i do this? Reason i ask is because the WP ADMIN is http://www.website1.com/wp-admin..

thanks for your help.