Memory Upgrades for iMac 27-Inch (2012 - Mid 2015)
Memory upgrade: Apple iMac 2012/2013/2014 (Howto)
How to upgrade RAM iMac late 2013 21.5inch - break & fix MOVIE - YouTube
NEMIX RAM 16GB Kit (2x8GB Upgrade) DDR3-1600 SODIMM PC3-12800 for Apple MacBook Pro Mid 2012 / iMac Late 2012 / iMac 2013, Late 2014, Mid 2015, Mac Mini Late 2012 at Amazon.com
A-Tech 32GB Kit (4x8GB) RAM for Apple iMac (Late 2012, Late 2013, Late 2014, Mid 2015) | DDR3 1600MHz PC3-12800 SODIMM 204-Pin Memory Upgrade at Amazon.com
21.5 inch late 2013 iMac - RAM upgrade - Apple Community
iMac RAM upgrade: Here's an affordable way to improve multitasking - CNET