A subdomain is the first portion of the URL that is present across all of your pages in your account. For example:
WARNING: Changing a subdomain will break any existing URLs. So proceed with caution. After updating a subdomain, you'll need to go republish any previously published pages.
To update your subdomain, follow these steps:
Hover your mouse over the gear icon in the upper-right-hand corner of your account
Select Organization details from the dropdown menu
Click the Edit Settings button
Scroll down to edit the Subdomain
Click the Save button
