In the main, Properties screens consist of a set of property names and property values, the values generally being maintainable by an administrator; where a value cannot be set by an administrator, it will not even be editable in the Editor.
In order to change the value of a property, simply type in the new value and either hit the 'Enter' or 'Tab' keys. Hitting the 'Enter' key will in most cases update the value and keep the focus in the current property value field (the exception being multi-line fields like 'Description' properties where 'Enter' will add a carriage return to the property value), whereas hitting the 'Tab' key will update the value and move the focus on to the next property value field, if any.