I paid the 2.24 for the upgrade and it's not unlocked.
Only the developers have the possibility of handling this situation because you've paid to their program. There is a support page created by them in the even that you need help with the software or with the payment towards them. Access the page, then use the email to contact them to ask for further information. No one else will provide support except them.
Contact page: http://thinkersoftware.com/photo-to-sketch/support.htm