Upgrading your processor typical means you will also need to upgrade your motherboard and ram so that each can work together. Although this can be expensive compared to a cheap ram upgrade you will notice the most improvement in performance by upgrading your CPU.
Power down your PC and switch it off at the wall. Remove the screws holding the sides of the case on and carefully slide off both panels.
Wearing an anti-static wristband is preferable whenever working with sensitive electrical equipment. Keeping one hand on a metal part of the case will have the same effect, though you may need oth hands when installing certain items of hardware.
Installing a CPU on a motherboard outside of the case if much preferred, as significant pressure must be applied to secure the heatsink which can bend and ultimately damage motherboards if they are not properly supported. You can install a CPU inside the case, though extra care must be taken not to damage any components or apply too much pressure to the board when fitting.
If you wish to remove the motherboard, you will need to remove all the expansion cards by unscrewing the backing plates and sliding them out carefully. You will also need to remove anything plugged into the motherboard, such as power cables, fan cables and so forth. It may also be easier to remove optical drives if space is tight, though generally this isn't essential to remove the motherboard.
Next, undo the screws holding the motherboard to the case and lift the whole board out onto an anti-static surface. If you're lucky, your motherboard may be secured to a tray, in which case it will just lift out once you have removed the cables and expansion cards.
If you are replacing an old CPU, you will first need to remove the old heatsink and CPU. You can do this by pushing down on the retainer clips with a flat bladed screwdriver on old-style heatsinks, or by pulling the lever up on the newer ones. You will need a reasonable amount of pressure to do either of these, which is why performing this task on a fully supported, flat surface is preferred.
Once you have released the catch, gently remove the heatsink and fan assembly. If the PC has been on recently, the thermal grease may still be tacky and require you to pull the heatsink off with a little extra force.
Next, lift the small metal lever pictured, which will release your CPU. Remove the CPU holding the very edges and lay it on an anti-static surface.
Now you are ready to install your new CPU. Remove the chip from its plastic case and check which corner the marker is on. Line this up with the CPU slot on your motherboard and drop the chip in place. You should not need to apply any force at all, so if it fails to drop into place, check you have the pins lined up correctly and the marker on the CPU matches the marker on the slot. Also check that the metal lever is upright (which it may not be if you are installing the CPU in a new motherboard).
Next, push the metal lever down which will secure the CPU. Now you must install the heatsink and fan, which may have come bundled with the new CPU. Most new heatsinks contain a small block of thermal paste which will melt onto your CPU and form the necessary thermal connection as soon as you turn your PC on. If this is not present, you will need to apply a small drop of thermal grease or paste to the die of the CPU (The small chip in the centre of the CPU).
Next, place the heatsink over the CPU and secure it using the lever or clip. The lever arm must be pushed all the way down and clipped under the plastic, which will need significant pressure. The older style heatsinks clip to the board using a metal bar.
This must be hooked over the plastic clip on one edge and forced down using a flat-blade screwdriver on the other. Once fastened, ensure that the heatsink is fitted securely, and plug the CPU fan into the appropriate power connector located on your motherboard.
If you removed your motherboard from the case, you will now need to put it back in. Secure the board with screws and replace any cables and expansion cards.
Finally, replace the sides of your case and boot your PC up. POST should show your new CPU, though you may be asked to enter the BIOS to confirm the speed of the new CPU. If you wish to double check, you can go to Start - Settings - Control Panel - System and check the reported CPU make and speed.