Upgrade iMac Intel Core i3 CPU to Core i7 - iFixit Repair Guide
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
NEMIX RAM 32GB Memory Upgrade Kit (4x8GB) DDR3L 1600MHz PC3L-12800 CL11 SODIMM Compatible for Apple iMac (Mid 2011, Late 2012, Late 2013, Late 2014 Retina 5K, Mid 2015 Retina 5K) at Amazon.com