iMac Core i3 3.2GHz (Dual core) upgraded to Core i7 2.93GHz (Quad core)
Upgraded my mid 2010 27 inch Apple iMac from a Core i3 3.2GHz (Dual core) upgraded to Core i7 2.93GHz (Quad core) processor. While I was in there, upgraded the Hard Drive from a 1TB drive to a 3TB drive and upgraded the RAM from 4Gb or RAM to 32Gb of RAM :)
Used iFixit teardown guide, iFixit heavy-duty suction cups (pair) and iFixit toolkit to upgrade my iMac. Worked like a charm.
Step-by-step pictorial guide is here - Upgrade iMac Intel Core i3 CPU to Core i7
Don't be a-skeered. It was easy. Just take your time and follow the excellent iFixit guides.
3TB HD is Western Digital, RAM is Komputerbay 32GB, Processor is Intel Core i7 870 2.93GHz 8MB LGA 1156 Quad Core Processor 95W