How to Set a Limit on the Number of Submissions
In certain scenarios such as contests or application forms, you may want to set a limit on submissions.
To do this access the desired form (How to Access Form) and head to the 'Publishing' tab.
Scroll down until you see options and check the box which says 'Disable this form after...'
In the right-most panel you will need to enter the number you wish to limit submissions to as well as the custom message your user will see after that limit is reached.
Form changes will save automatically.