I have searched Stack Overflow, Stack Exchange, Super User, and didn't find anywhere an option to change my email address. Is there a way to do so? The email address I have provided at registration will be deleted today, therefore I have to change my login details on all sites.
You might find this Help Center page useful. It explains how to add additional email addresses/logins to your StackExchange account. You should also be able afterward to remove old, unused/unavailable email addresses/logins once the new ones are verified.