Hello Bjorn,
you can use the service manager and RETRIEVE the instance with IV_BEFORE_IMAGE=true and false. Afterwards you can compare the both images/data if you would like to derive the attributes that have been changed in the current transaction. If you would like to just react on UPDATE, you have to filter the changes accordingly in the event handling action.
Of course, implementing an own, more specific event handling functionality on your own is also a valid approach.
Best regards
Tilmann