You've built a form and you've had workers submit forms against it. If you want to edit the form, say remove a question you will find that question delete button is disabled. This is because you cannot delete form questions with results against it.
To remove form questions from a form, you will need to copy the form and archive the old one:
Go to Forms > Select Form and click Copy
In the copied form you can now delete the form question and add in a new one.
Tick the Publish box
Click Save and Close
Archive the old form
We suggest that you start to use version numbers to keep track of updated forms i.e.
Pre-start V1
Pre-start V2