If you have admin access, you can enable the Field UI module and change default values and required field settings via the Drupal admin UI. https://www.drupal.org/docs/7/core/modules/field-ui
I’m tempted to caution against this though, unless you have a very good reason, and know how to maintain these overrides alongside updates to farmOS. Could you describe a bit more why you want to do this? What are you trying to accomplish from a workflow perspective? Maybe I can help by suggesting alternatives.
The “proper” way to do this would be to write a module that alters these things, without touching/hacking the core farmOS code. This is one of the golden rules of farmOS (and Drupal): “don’t hack core” - don’t modify the farmOS code itself, unless you are proposing an upstream change. Otherwise you are essentially managing a fork of the software, and any changes you make need to be recreated every time you upgrade to a new version. A module, on the other hand, can be managed as it’s own code repository that simply “hooks into” certain parts of the farmOS/Drupal code and makes alterations.