Removal of CPU
There are several types of CPU fan / Heatsink assymblies on the market these days, usually there is a lever, or two on either side of the fan that tension the fan and heatsink to the CPU socket. Once released the fan/heatsink should come off as a single unit. Sometimes you may need to gently " wiggle " the fan/heatsink in a rotating motion to loosen it from the CPU thermal grease.
Once the fan/heatsink is removed, the CPU slot will have a single lever on one side, this can be lifted, and the CPU should come out of the socket.
Remember to gently place the new CPU into the socket, it should only seat properly one way, so remember to note how the original CPU was seated.
Apply a very thin film of thermal grease to the top of the CPU*, and re-attach the cooling fan / heatsink unit.
*Thermal grease is quite inexpensive, and easy to apply, put a small dab in the center of the top of the CPU, and with a small flat piece of plastic such as an old credit card, smooth the grease out and spred it to the edges of the raised surface of the CPU.