From Ross-Tech Wiki

4.4 How do I upgrade my existing VAG-COM software to the newest version?
You should be able to simply Download and install the latest release of VAG-COM in your PC. All of our Current Interfaces have built-in Activation, so the new version should be fully Registered and Activated once you test on a car. If you'd like to be notified when a new version of VAG-COM becomes available, you should sign up for our Announcements List.
For our older Interfaces without built-in Activation, or for 3rd party Interfaces:
The new version of VAG-COM should see and use your existing registration/activation. Very rarely, the software will revert to shareware when an upgrade is done. If you perform an upgrade and feel it killed your registration, simply complete this short form to request a new activation code. Requests submitted via e-mail, fax or telephone, or forms with incomplete information will be rejected and will delay your activation
If you purchase a genuine Ross-Tech Interface directly from us, or from one of our Distributors, you are entitled to free software updates for at least one year from date of purchase. Compatibility of future versions of VAG-COM with 3rd party interfaces is not guaranteed.