You can easily delete a form by following the steps below.
1. Login to the admin portal
2. Click on the My Forms button
3. Find and click edit on the form that you wish to delete
4. Click on the "Advanced Options" button
5. Then Click Delete Form at the bottom.
If you have accidentally deleted a form and need to recover it, you can follow the steps outlined in this article Recover Deleted Form
If you have any questions please feel free to reach out to firstname.lastname@example.org