Transferring existing Venture theme site to another url
I have a client who originally wanted their web site to be built on a different domain, and then have a secondary domain point to the new site. So now, the secondary URL forwards to the primary URL.
This works well, but the secondary URL is more popular and when you go to the site it has a different (the primary) URL in the web address bar. We masked the URL to prevent confusion, but still received complaints/confusion from visitors.
We've now decided to make the secondary URL the primary web address, so I am looking for the easiest way to do so. The site has the Venture theme on it. What is the easiest, quickest, and least disturbing way to make such a transition?
Thanks in advance for any help!