Make sure you get the correct upgrade from CS & CS2 to CS4. Avoid CS3 to CS4 upgrades, otherwise the installer is going to ask you for a CS3 serial which you don't have. So, you would need to know the exact Manufacturer Part Number, try to speak to Adobe customer service (not that I think they're going to be much of help) 1-800-833-6687 and ask for that number.