During your initial boot-up, most computers tell you which key to hit to access the "setup" which is the BIOS setup. Look either at your screen (closely) and read the fine print during bootup, or if that doesn't reveal which key, consult your user guide. (You might have to boot up more than once to catch the instructions for accessing setup, depending on how long that screen is displayed.)
Below is a link to instructions which may be of help on setting up your BIOS. The memory is covered in PROCEDURES, STEP 4 and is referred to as DRAM.
http://www.pcguide.com/proc/setup/biossafe-c.html
Your failures could also be related to how your computer is set up. You might want to take a look at the link below and run through the setup instructions to optimize your computer.
http://support.microsoft.com/default.aspx?scid=kb;en-us;308417
A other thought, make sure you are NOT running any other programs when you are gaming. If it still crashes then you know for sure it's the gaming "stress" on your PC, or a problem with the gaming software. Look in the bottom right corner of your screen. You will see numerous icons. Right click on them, one at a time and left click on EXIT. DO NOT close your anti-virus or firewall (if you have them). Close all other applications before starting your game.
Also, I'd try the performance optimization first and not go into the BIOS until you're sure you have to.