How to change account from free to free professional trial

Hi - I am currently using the free version but I'd like to trail the professional version to decide whether or not to upgrade. I signed up a few days ago, but I want to change it from a free version to a professional evaluation version, but I can't change it. What should I do? It hasn't been long since I signed up and I don't have much content, so should I leave and re-subscribe with the same ID?