How to remove collaborators and restrict access to a form

When you create a collaboration link it adds an API key in your profile settings. Once you are finished collaborating you can delete the key. This will remove all collaborators.

For example:

Thank you so much for the answer, however I can't tell how you got to the section where you removed the collaboration key... where are all those lovely options? 

The is an API page on the My Account page. Here is the link of the API page - https://www.jotform.com/myaccount/api 

Feel free to contact us if you have any other questions.