Apple Technician Guide Imac (27-inch, Mid 2010) -

Common in older units due to dust. Re-applying thermal paste to the GPU and CPU can significantly reduce operating temperatures.

Up to 3.6 GHz Intel Core i3 or i5 (Dual-Core); up to 2.93 GHz Intel Core i7 (Quad-Core). Apple Technician Guide iMac (27-inch, Mid 2010)

When replacing the HDD with an SSD, you must use a specific thermal sensor cable or third-party software (like Macs Fan Control ) to prevent the internal fans from running at maximum speed. Common in older units due to dust

Detailed, step-by-step guides are available from iFixit and PowerbookMedic . Apple Technician Guide iMac (27-inch, Mid 2010)