replacing Transmission Filter

I have a 2000 malibu, under stress on hills or with a load, the transmission seems to slip, mostly in 4th gear. (auto). I picked up a new filter, gasket, seal and fluid to start there before I do any tranny work I'm not looking forward to doing. Does anyone have any tips, ideas or directions in changing these. I have a jack and jack stands, but no lift. I'm not certain on if the engine should be running or not and if so, when? Any help would be great. Thanks.
-Street