Yes, you can always make changes to your form.
If you have already collected results and need to make major changes to the form, we recommend making a copy to keep the old form and its results intact. You can then change the Directory for both forms on the "Share" page to keep the form link the same.
If you need to make minor changes to the form, such as editing a single item, be aware that the new settings will modify your existing results. The recommended process for editing items on an already-published form is to make a copy of the item, edit the copy as needed, and set the old item to Admin. Admin items do not appear on the form and are only seen in the results table, so your previous results will remain intact.
For more information visit the Admin documentation page.