How to update processor?

If you are 100% certain that it is your processor that needs upgrading, you need to know what your socket size is. There are a number of free utilities you can run which will tell you this information if you don't know it already. I use PCWizard. http://download.cnet.com/PC-Wizard-2008/3000-2094_4-10793737.html

Then make sure you have some thermal paste and simply change out the processor. There shouldn't be any configuring needed. The processor you want to get will depend on what type of workload you're going to be running on the computer, what applications you will be running, etc. I have a personal preference to AMD processors over Intel. And with Vista as your OS, I would get a dual-core of some sort.

Hope this helps.

All you need is sisoftware sandra:
http://www.sisoftware.net/
Install the CPU, step by step:
http://www.pcmech.com/byopc/step-5-install-the-cpu/

This software will tell you which processor you have so that you can then find the latest processor for your motherboard.