What is JotForm?
JotForm is a free online form builder which helps you create online forms without writing a single line of code. No sign-up required.
At JotForm, we want to make sure that you’re getting the online form builder help that you need. Our friendly customer support team is available 24/7.
We believe that if one user has a question, there could be more users who may have the same question. This is why many of our support forum threads are public and available to be searched and viewed. If you’d like help immediately, feel free to search for a similar question, or submit your question or concern.
Unfortunately, you cannot change the type of the field in your form.
In this case you'll have to add the checkbox to your form.
Please let me know how to do that without losing all of my data.
I suggest that you hide the radio button. This will allow you to keep the captured data from this field and it will not be shown in your form once is hidden.
Right-click it and click on Hide Field.
Please let us know if you have further questions.