Power off the computer and remove the power cord from the power supply
remove the both side covers off the computer
inside you will see the harddrive towards the front probably under the cd rom or a drive take off the cords attached to it i recomend labeling them for identififcation purposes then get a phillips screwdriver and remove the screws that are holding the harddrive in place ow just slide the harddrive out and install the new one put all the screws back and the cables back the way they came off then put the side covers onn and you are done