There should be another letter after the DS3 - 'P', 'R', or 'L' - need this to identify your board. Also, at least one of these boards has more than one revision - this info may help, as well. You can find it here:
That said, I'll try to point out a general procedure for finding this adjustment. When your system boots, it will likely show one of two screens - this one:
for which you need to press <TAB> to get to the next one, or it may start with the next one:
Once at this screen, you will need to press <DEL> to enter the BIOS:
where the "Integrated Peripherals" page contains your RAID settings...