Want to change CPU in a 2009 27"

I have bought a 2009 27" for repair, and I want to change the original i5 (LGA1556 2.66) CPU. The Logic board socket is LGA115X. Does it means I can use any LGA1150 CPU or have I to use the original socket LGA1156?

Does anyone know anything about this kind of upgrades?

Thank you