Hello! (Apologies for the slow reply — I was visiting with family last week!)
We don't retail imitone studio on Itch, but we have an upgrade service available here: https://imitone.com/support/#upgrades
The process is not automated so give us a bit of time to fulfill the order. We will cancel your existing license and issue you a new one. You can speed up the process by sending an E-mail with your 16-digit key to support@imitone.com after you place your upgrade order.