Go into the BIOS look for DRAM or DIMM frequency and make sure its at 800 or 1600 (depends on your BIOS) , then manually key in the timings ex :7-7-7-20-27-1T and then go to the DRAM voltage and set it to whatever is specified by the manufacturer....
^^^^^^^^ it does not get any easier than that ^^^^^^^^
What do you mean by change the BIOS? Update it? If so, aren't the instructions to do so on the manual? The updates themselves should be available from the Asus website.
Go into the BIOS look for DRAM or DIMM frequency and make sure its at 800 or 1600 (depends on your BIOS) , then manually key in the timings ex :7-7-7-20-27-1T and then go to the DRAM voltage and set it to whatever is specified by the manufacturer....
^^^^^^^^ it does not get any easier than that ^^^^^^^^