To delete a form navigate to the Ecollect Forms page from the Admin start page. Locate the form you want to delete and click on the icon with the red circle with a line (shown below) to delete the form.
Disclaimer: Deleting a form will delete all responses and will remove any analytic abilities. Ensure you are sure this is what you want to do. If the form you are deleting contains "linked" fields to student fields, the student record will remain intact and no changes will be made to the student record.