Here's an overview if you have to do any work when upgrading.
Dropped support for Symfony < 2.6 and added support for Symfony 3.x.
The internal implementation of the Google Authentication and email authentication method has been re-factored. If you depend on internal classes, please check if your code is affected.
Changed case of parameter from $GoogleAuthenticatorSecret to $googleAuthenticatorSecret in Scheb\TwoFactorBundle\Model\Google\TwoFactorInterface
The default authentication form template requires a route _security_logout to be defined, that directs to your logout URL. Alternatively you can configure a custom template.