This is particularly useful if you’re moving from Squarespace 7.0 to Squarespace 7.1.

1. Disconnect your existing domain from your old Squarespace website.
   Settings —> Domains —> Disconnect

2. Then go to your new website, Settings —> Domains —> Use a Domain I Own and reconnect your domain (it will likely have you login to your registrar).

Note: the easiest transitions are domains registered at Squarespace or GoDaddy. Other providers may require you to update DNS settings manually. Allow about 24 hours for the reconnection to happen (though it’s often just few hours).