first I wouldn't change the field type to the yes/no.
Allen Browne: Why I stopped using Yes/No fields nor actually store that as text in your database.
Option buttons will not return text values.
You can use conditional function in your forms and reports to show "Yes" or "No" to the user on an as needed basis.
Shem K's suggestion is one option provided you need to update values/choices; however, may not really be needed depending what you are attempting and can be... well... difficult down the road, once again, depending on your application.