Apple's 27" iMac Late 2012 model. How to upgrade the ram to 16GB - YouTube
Install memory in an iMac - Apple Support
Install memory in an iMac - Apple Support
Can you upgrade the RAM in the 27-inch iMac? | iMore
Timetec 16GB KIT(2x8GB) Compatible for Apple DDR3L 1600MHz for Mac Book Pro(Early/Late 2011,Mid 2012), iMac(Mid 2011,Late 2012,Early/Late 2013,Late 2014,Mid 2015), Mac Mini(Mid 2011,Late 2012) MAC RAM at Amazon.com
How To Upgrade RAM on the Apple iMac 2012 - 2013 RAM Upgrade - 21.5 inch model - YouTube