How do I return my activation code in oder to upgrade software?

Hi,

I have just purchased an upgrade from Trados Studio Starter 2015 to Freelance. When I try to process the upgrade (same computer), I get the following error message:

"In order to process this upgrade, please return any in use activations."

How do I return my activation code and where do I get a new one from?

Thank you very much for your help!

Aneta