Setup: I need to change the format of a custom question
I defined my custom questions using a check box/drop down/radio button and can see now that it is not what I wanted.
If you already have registrations, you can't change the type of custom questions from one format to another.
If all of your registrations are Preview/ Test registrations, just delete them - See: Delete test registrations
If you have registrations that are NOT all test registrations, you can add a new/ revised custom question and Disable the existing one.
See also: Disabling a question or additional item