CPU upgrade in base 2011 21.5" iMac?

has tried upgrade i5 in base 2011 imac 65w i7 processor? apparently works models had upgrade options (but base model didn't), haven't heard definitively 1 way or other if can upgrade base model.

 

20 seconds googling produced this: http://www.ifixit.com/guide/installing-imac-intel-21-5-inch-emc-2428-cpu-replacement/5951/1

don't know exact imac have might not work if have earlier model.

 

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