Google Authenticator and a New Phone – Changing Devices

gragib says:

There is a very simple solution.

1. Under Security, click on Edit in 2-step verification.
2. Under How to receive codes and Mobile application, click on Remove/Replace and follow the instructions.

You will be issued with a new QR code and the sequence for the verification code will be reset. Your Application-specific passwords (if any) will remain unchanged.
Via theverge.com.