The proper way is after pointing the new domain to your hosting account to change the URL references in the Database. So, besides the siteurl & home options you shouldn’t forget upload path at the same table and a complete search & replace for local links and media URLs inside post contents.
There are many ways to do this according to the Codex.
Lately I’ve been using the WordPress Search & Replace tool that can scan all required tables to replace the URLs. ( Always backup the DB first )