Please don't get under the car if it's only on a jack... use properly rated jack stands b/c you never know when a hydraulic jack WILL fail.
Then just follow san resho's tip - it's the easiest way w/o a lift. Also, be careful to not drop your drain plug into the catch pan (unless you have a separating grate) and oh yeah, make sure your catch container can hold at least 10 quarts/liters b/c you'll never get the drain plug back in should it over flow
Good luck
