change website (hiding)

Hey there,

You can build your website on localhost, or a sub-domain, so users will see the old website until your new one is ready to go live. Take a look at this tutorial if you wish to create your website locally first, and then upload it when it’s completed.

Hey there,

is it more difficult to move
http://www.old.com to http://www.new.com

than to move
sub.new.com to http://www.new.com ?

No, both require same level of knowledge. Neither is more difficult than other, moving a WordPress installation from a sub-domain to main domain or from a completely different domain involves same process. Hope it helps.