We've made it super straightforward for creators to change the version attached to a customer's purchase after they've made it.
This can be done in lieu of a refund in case a customer made a mistake (e.g. selecting Mac instead of Windows), or if you want to give folks a free upgrade. Once the change is made, they'll get access to the files of the new version instantly.
You can also use this feature to assign prior customers who purchased without selecting a version, to a version that now exists.
Note that this doesn't have any monetary changes. It only updates the content that the customer will have access to. Just hit "resend receipt" after you save to remind them of their unique download link!
Sahil and the Gumroad team.