If a possessory title is given on an adverse possession application, it was because there were unanswered questions regarding title at the time of first registration. To convert title, it will be necessary to answer those questions. It will not be a straightforward conversion application. The Statute of Limitations does not run on the possessory title, so time will not cure the matter either.
Think long and hard about this one - there is a possibility that the title is worthless.