How to Upgrade Memory in a 21.5-inch or 27-inch iMac (Mid 2010) - YouTube
Install memory in an iMac - Apple Support
Install memory in an iMac - Apple Support
NEMIX RAM 32GB (4x8GB Upgrade) DDR3-1333 PC3-10600 204-Pin SODIMM Memory for Apple MacBook Pro Early/Late 2011, iMac Mid 2010 27 inch 4-Core, iMac Mid 2011 21.5/27”, Mac Mini Mid 2011 at Amazon.com
APPLE IMAC 2010, ALL-IN-ONE, 21″ inch Full HD , CORE 2 DUO, 2.26GHZ, R – Montag Store