Memory Upgrades for iMac 27-Inch (2012 - Mid 2015)
Install memory in an iMac - Apple Support
How to Upgrade Memory in a 27-inch iMac (Late 2012-2013) iMac13,2 and iMac14,2 - YouTube
Apple iMac 21.5" Core i5-4570R 2.70 GHz, 8GB RAM, 1TB HDD, 10.15.6 Lat – Pc Retro Shop
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