Core 2 Duo / Quad uses different sockets than the Core i3/i5/i7 CPUs.
In fact, depending on which Core i generation you are talking about they use (from oldest to newest) socket 1156, 1155, 1150. That excludes the "Extreme" version which uses socket 1366 (older) and socket 2011 (current). They all require DDR3 RAM as well.
An upgrade means new CPU, motherboard and RAM.