Yes, you can do so in the form builder. However, if you have already received applications, please note, that the ones who have already submitted, did so using the previous version of your form and cannot change their application. Best to make sure to test the form thoroughly, before launching the official call for applications.
Minor changes, such as adding a helper text or re-phrasing existing questions for a better understanding, are no problem at all. Simply click on the form builder on your admin dashboard, select the question to adjust and publish the changes.