I advise against attempting it unless you have the right equipment. Here's the technique I use to replace driver chips, and it should work with processor chips too. You will need:

Electric hotplate Thermocouple temperature measuring device. I use the thermocouple attachment on my multimeter. Hot air SMD desoldering tool with a square nozzle about the right size for the chip. Vacuum pick up tool. Very cheap on eBay. Fine tipped tweezers No-clean flux pen Isopropanol spray Cotton buds Fine-tipped soldering iron Solder wick Strips of corrugated cardboard covered in Kapton tape - probably not needed when replacing a processor

Use the strips of Kapton-covered cardboard to mask Molex connectors and other sensitive parts near the chip to be replaced from the hot air. Place the board on the electric hotplate with the thermocouple probe underneath it and adjust the hotplate to get a reading of 100 to 120C on the thermocouple. Wait several minutes for the board to come up to temperature. This makes desoldering easier. Heat the chip with hot air at about 260 to 300C until you are quite sure that the solder has melted all round. Gently lift the chip off with the vacuum pickup tool. As Tony says, it is easy to lift the fine traces off the board if the solder is not completely molten all the way round.

To fit the new chip, apply no-clean flux to the pads. Drop the chip on the pads, the right way round, using the vacuum pen. Nudge it with tweezers until it is perfectly aligned with the pads. Heat the chip with the hot air until the solder is molten again (about 20 seconds), then remove the hot air and gently press the chip down with the tweezers, taking care not to shift it sideways. Remove the hot air and turn the hotplate off. Allow to cool.

Check under magnification that all the pins are soldered down and there are no bridges. Touch up any bad joints using the flux pen and fine tipped soldering iron, and remove any solder bridges using solder wick. Finally, use isopropanol spray and cotton buds to remove surplus flux.