Changing the clock battery on a computer.

This is not a difficult job. Just be sure to unplug the power from the PC first and touch the metal case to discharge any static charge before touching the motherboard.
Here's some more help:
http://www.liverepair.com/encyclopedia/articles/cmosreplace.asp

Hello,

This should be a very simple process.

Just open the case, their should be a button on the top rear and bottom rear of the case, press both and case will split open.

Picture below of battery removal:

Diagram may not be exact, but you should be able to pop this out with your fingers or a small flathead screwdriver