Fields that are populated by the system and cannot be edited by users include record information fields such as record ID, Updated By, Last Updated [Date], Created By, and Created Date.
However, the "Type" fields (Contract Type, Organization Type, etc.) may be edited but must be unlocked first. To do that, click 
which changes to
. You may then select a new value from the drop-down. The field will lock automatically after you select the new value.
CAUTION: Selecting a new type changes the layout (fields, sections, etc.) to match the new type.