This answer was pulled from another post on this forums however:
1. Determine what socket the CPU uses. Basically all "U" (like i5-4210u) and "Y" (like i5-4220y) model Intel mobile CPUs uses socket FCBGA1168. "BGA" basically means the pins are meant to be soldered into the motherboard and you cannot upgrade it.
All other models like "M", "H", "MQ", "HQ" and "MX" should be socket FCPGA946 which means they actually go into a socket and can technically be upgraded.
Information was taken from:
http://www.tomshardware.com/answers/id-2372970/laptop-cpu-upgrade.html