Hi there,
Quite often, when upgrading RAM, it is really a case of suck it and see, I'm afraid. If the RAM you are going to add is the same speed as your existing modules then you shouldn't really need to make any changes to the BIOS.
If it is of a faster speed then it will be pulled back to match the slowest speed. If it is slower, than your existing RAM will be slowed down to match.