Yes we have done this many times. If you bought it originally from Disney, you shouldn't have any trouble. There has been some reports of difficulty upgrading
undercover tourist purchased tickets.
I would recommend using the ticket to enter the park and then head to guest services to upgrade to
DVC APs. Just be sure to take picture ID and your DVC cards with you. I f you use them to enter the park, you get credit for today's price of a one day pass, not what you paid a few years ago. Unless this has changed. But we did this last march with no issues.