Ursprünglicher Beitrag von: Dan ,
Sadly you can't swap out the GPU unlike the older 2011 models and older. From 2012 'Thin Series' use a soldered down GPU chip on the main logic board. Here is the teardown for the slightly older system for reference: [guide|30260|iMac Intel 27" Retina 5K Display Teardown] Jump down to Step8 for an over view of the chips on the logic board. Apple only did a slight upgrade to this system for the 2017 model.