A-Tech 32GB Kit (4x8GB) RAM for Apple iMac (Late 2012, Late 2013, Late 2014, Mid 2015) | DDR3 1600MHz SODIMM PC3-12800 204-Pin SO-DIMM Max Memory Upgrade at Amazon.com
Memory Upgrades for iMac 21.5-Inch 2012 - Late 2013
How to upgrade RAM iMac late 2013 21.5inch - break & fix MOVIE - YouTube
iMac RAM Upgrade mixing different memory sticks: 27” iMac late 2013 - YouTube