1. How do I edit a farm already listed?
Once you are signed into your account, go to Account Settings , and click on "My Locations".  Click "Select" next to your locations name.  You will now be able to expand sections on this page by clicking on the sections blue header to view and/or edit that sections information.  If your location is not listed on your "My Locations" page, you will need to "Join" that location.
This YouTube video may help you: