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 upgrade: Apple iMac 2012/2013/2014 (Howto)
New 21-Inch iMac Won't Let Users Upgrade RAM Themselves, But 27-Inch iMac Will | Cult of Mac
Can you upgrade the RAM in the 27-inch iMac? | iMore
How to upgrade RAM iMac late 2013 21.5inch - break & fix MOVIE - YouTube