I recently downgraded from Pro to Basic without filter. I just emailed support@glowforge.com with my request, we exchanged a couple more emails to hammer out the details, and a few days later they sent me a check for the difference. They sent a check because I originally payed with PayPal and it had been more than a year since my purch… it had been a year since the original transaction.
The amount refunded was reflective of the price at the time, not of current prices. (I assumed that would be the case, but it was a question I had so I figured I’d pass it along in case anyone else had that question.)