Rick, I don't think that there is a simple answer to changing a battery on a PC. There are a number of batteries used to start off with.

I have only changed one for somebody else and that was easy - just take the case off and one just unplug the leads from the battery and swap. I have got the cover off my PC at the moment and looking at mine, at a minimum, I would have to remove the hard disk and A drive just to gain access and even then it looks as if it would be very fiddly. I would suggest you note the model and ask a computer store for advice.

Jon