Move directory

Basically I have a forum to platform vBulletin 5 and I want to transfer it to Xenforo. But I do not want to miss our posts and topics, I found a company that makes such a transfer.
The problem now is that since you doing the installation and transfer the data to another company in Xenforo, How you turn the Xenforo appear at the correct address;
Example Now the Vbulletin forum is www. , for the migrating , need 2 plarforms online the old (vbulletin) and the new (xenforo) After the migrating How will become the new forum to appear on the correct address(

Thank you