If you purchased the AP at full price and now want to get the discounted PAP, you may be able to do it at no cost. The AP pricing last year (pre-discount) was a few dollars lower than the currently discounted PAP cost. There have been many reported instances of Disney CMs allowing
DVC members to upgrade their pass at no charge. I did it myself back in May.
That said, there have also been scattered reports of folks being denied the upgrade. In one recent post, an individual was told that CMs should never have been doing the upgrade and they had now stopped it as a practice. Personally, I doubt this is entirely true. If they'd have stopped it after 2 weeks, I could see the logic. But I don't see why they would change the policy 6 months in.
If you get declined, be persistent. And don't forget to take along your blue member card and a photo for each pass being upgraded (except the kids, of course.)