I have the Lenovo Thinkcentre M82. The motherboard should support Ivy Bridge straight out of the box without a BIOS upgrade. Also, in the used market here where I live, the i5's are like 3x cheaper than the i7's.Yes, it would help performance SOMEwhat. Better by far would be an i7-3770 or 3770k, but even the i5 would be a definite upgrade.
But the FIRST thing you need to do is verify that your motherboard even supports that upgrade.
What is your motherboard model number OR the model of your prebuilt system. The EXACT model. For prebuilt systems there should be a sticker with the exact model AND sub-model or express service tag that will tell us. For motherboards, it should be printed directly on the motherboard itself either along the top edge above the CPU socket or down the middle of the board in most cases.