It is not currently possible to change the registration type of a record in a registration form.  The established record is tied to the registration selections made when it was created.

Delete and request a reregistration, if possible.

Blackbaud has an idea bank our clients can go to and list any suggestions they have for our programs. You can go to http://sphere.uservoice.com/forums/143074-sphere-product-whiteboard/ to enter suggestions and vote for you favorite suggestions as well. This is a direct line to our programming team and they look at this for enhancements to the software.