To install a new processor, start by disconnecting all cables and wires connected to the CPU cooling fan. Carefully remove the CPU cooler, and pull out the computer's motherboard. If you're installing an Intel CPU, rotate all four mounting pushpin caps to the left. Next, gently pull each of the pushpins straight up until you feel them release.
Push down the lever on the side of the socket, pull it slightly to the outside and release it upward. The socket cover should swing open. Next, align the notches on the two opposing sides of the new CPU with the tabs on the socket and gently lower the CPU into the socket. Close the latch over the socket, apply thermal compound over the surface of the CPU, rotate the heat-sink latch covers to the right and pull them up. Align the four pushpins with the mounting holes in the motherboard.
Keeping the heat sink steady, push the pushpins in diagonal order until they're latched in order. Next, attach the heat-sink fan connector to the assembly. Reinstall the motherboard and reattach any wires you disconnected at the beginning of the installation process. A similar procedure applies for installing an AMD processor, except that contact pins are on the CPU rather than in the socket.