You can deactivate your product yourself if you have Photoshop or Elements.
Choose Help->About Plug-In->ProductName... (Windows)
Choose Photoshop->About Plug-In->ProductName... (Mac)
Choose Elements->About Plug-In->ProductName... (Mac)
You'll find a de-activate button on that dialog.
Deactivating on one machine will allow you to activate on a different machine.
If you have a different imaging application then please submit a ticket and we can de-activate it for you.