OWC SSD Upgrade Kit For 2010 27-inch iMacs, OWC Mercury Electra 250GB 6G SSD, 18" SATA III 6Gbps data cable, SSD Power Cable, Installation tools and iMac screen adhesive tape set :
How To Upgrade HDD on Old iMac 27 Inch 2010 Faster SSD Samsung SATA 2.5 - YouTube