Surprisingly easy to fit.

Locate the RAM slots on your motherboard - they should be located near to the top of the motherboard. If necessary move the hard drive ribbon cables to one side to obtain a better view (taking care not to disconnect them).
Push the retention clips at either end of the slot outwards (these clips are used to secure the RAM in the slot afterwards) to allow you to slide the chip in. Make sure you use the spare slot nearest to any occupied slots (check yoru motherboard manual). If removing any existing RAM, the action is the same - it should cause the chip to raise up slightly from the socket. Once free, the RAM may be lifted clear of the slot.
Next, align the chip you are putting in so that the cut-outs along the connecting surface align with the notches in the bottom of the RAM slot (they will only line-up one way round) and then firmly push the chip into the socket.
The retention clip will automatically swing back in toward the RAM chip once the chip has been pushed fully home. If you find that this chip is still out, try re-aligning the RAM and then pushing it in again.
This part is the moment of truth. Reconnect any cables you've unplugged. Switch the computer on and, as the machine boots up, watch the BIOS screen (this is the display of your machine's specs). It should display the total amount of RAM that is now inside your machine. If the figure is correct then you have successfully fitted extra RAM in your computer.
Please note that although upgrading RAM is a simple process, this is meant as a guide. This site cannot be held responsible for any damage done to a PC caused by a user. In addition to the advice given above, you should always consult your PC manual for any machine-specific instructions or advice. Fit this memory at your own risk.