You really need to do your homework on this. You need to know the motherboard type and what it supports, you then need to find a processor that fits within those specifications, and then you need to find out where it is and how to get to it.
For finding the processor type, there are many ways to do this. However, I would download a program called Belarc, it's free. Run it and will provide a report of your entire system, including all the specs on your processor and your motherboard.
From there, you might be able to find a YouTube video on how to replace it.