Drop in your ram, see if the computer boots. If it does 90% of the job is done. If you have problems, I think your best bet would probably be with the computer shop. I can give you rough instructions on how to mess around in the BIOS, but I would definitely not recommend fiddling if you're not comfortable with doing it.
Truthfully, you really shouldn't need any more than 8Gb for modern games for (probably) years to come.