To make a secondary website the primary website for a site collection (which associates the site collection's URL and any of its custom domain names with the new primary website):
- Go to the site collection detail page.
- In the Secondary sites in this collection section, find the website that you want to set as the new primary website.
- Click the website's Make primary button.
WARNING: Do NOT delete the "old" site yet. There's still one more step. Keep reading...
