Get it up on ramps or jacks stands, (make sure you have a pan gasket and filter kit first), loosen all the pan bolts on the tranny pan, get a big catch basin under it and try to drop one corner. Once most of the oil is drained, remove all the bolts and pull the pan down. Change the filter (it may have a couple bolts) and clean the inside of the pan. Scrape ALL of the old gasket off the mating surfaces, dry everything and put some gasket sealer on the pan flange. Place the gasket in position using the bolts to align it and press it against the sealer to hold it in place. Get a couple bolts in place, and get them started, being careful not to cross thread them. Get the rest in, finger tight only. Use a torque wrench to carefully torque the bolts down in alternating order (this is critical, the pan will get bent easily if there is misalignment and will leak forever). Once its tightened, fill it to within one quart of capacity (check your manual for the amount) with ATF, start it, shift P to L and back a few times and check for leaks. When the oil is warm, check the level (with the car on level ground) and add as much ATF as needed to get it into the operating range on the dipstick.
Or - go to the local Quick Lube and pay them to do it