It is AHCI. There is a place in the bios to set the sata mode. The other options will be IDE or RAID. You want AHCI so that windows-7 drivers will be used, and they can pass on the trim command.
I think you will find it in something like chipset configurations. It will be there somewhere, keep looking.
If all else fails, read the motherboard manual.
Which sata port you use really does not matter.