Since the upgrade is for users of P4 through P5, I would assume that it would look for either version before upgrading. That meaning if you had either 4 or 5 installed it would be OK. In the past, you didn't need either as the upgrade was just a discount at the time of ordering. The software was the same as the one sold in the store. There was never a seperate upgrade version and full version software. I would assume that is still the case. I still will need P4 Pro installed since this is the last version with a Lightwave plug-in.