I'm pretty ignorant about registered vessels, but here in
Canada I'm researching a similar question right now. From
what I've seen, you can start by checking the status of the vessel
registration by entering the
registration number in the Vessel Registration Query System (
click here).
The vessel can be removed from the Canadian registry at no charge. But to register her under your own flag and name, you will probably need an official Certificate of Deletion (for C$50).
Click here for details.