Depends on how comfortable you are in manually going into the DNN database. What you need to do is change the AuthenticationID of the DNN AuthenticationType in the Authentication table. Because it's a primary key you can't just edit it so what you have to do is make a copy of that record and paste it back into the table (so that it has a higher AuthenticationID. You can then remove the first record.

* Make sure you have a backup of your database before attempting any modifications. This will rescue you if things go sideways *