1. Click on the "Site Settings" link at the top of the screen
2. Click on the "Web Address" tab
3. Enter the Domain address you wish to re-map your site to
4. Click the Add button.

Some things to keep in mind about changing your site URL:

• Mappings are restricted to sub domain level only like www.example.com, wiki.example.com, or support.example.com. We don't support naked domain mapping like example.com.
• You can map up to 5 sub-domains to a given site
• This only takes effect for public sites private sites will redirect to the standard URL

Once you have completed the steps above, you will need to be sure to follow the next steps:

1. Sign in to your domain registrar.
2. Navigate to your DNS Management page. The location and name of this page will vary by host, but can generally be found in Domain Management or Advanced Settings.
3. Find the CNAME settings and enter the following as the CNAME value or alias: (sub domain)
4. Set the CNAME destination to the following address: ghs.google.com
5. Save changes with your domain host

If you are working with a site in Google Apps, see this article.