While the total fill level is 6.45 qts you'll need close to 9 to first drain the pan, and then refill it with 3 quarts. Then open a cooler line and start the engine while another three to four quarts is added to the system to replace what gets pumped out of the convertor. Then close the line and fill the transmission to the safe region on the dipstick with the transmission at the appropriate temperature. You should end up with a quart extra, but that's better than one short when you do this.
Be sure to use Hyundai Automatic Transmission Fluid Diamond SPIII.