Obviously your service uses optimistic locking and expects an If-Match header, containing the ETag of the entity, in the request. You can pass this ETag as parameter to the update method. For further details you should check your service definition and the documentation.
Regarding the update of header attributes: It is hard do answer as there is no information regarding your entity orchestration. Normally you should be able to add a property containing the update information for you header to the data structure you send to the server, e.g. if the header is reachable from your entity ZSystemName via association "Header" you do the following:
data.Header = { "attribute1" : value1, "attribute2" : value2 }
与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…