There are two types of UI fields, system defined and user defined. You need to have administrative privilege to make changes.
For system defined fields: To add or delete a field: Go to Site Admin->Parameters->System Fields Toggle, then you can check a field on or off. To rename a field: Go to Site Admin->Parameters->System Fields Rename, then change the field name. Make sure you click "Save Changes" in the end.
For user defined fields: Go to Site Admin->Customize Field, then add or rename a field. To delete an existing field, just check the "Is obsolete."