It depends on your vehicle. On most cars I've owned, you must remove all of the transmission fluid pan bolts as there is no drain plug. Care must be taken when removing the last couple of bolts so fluid runs into a collecting pan. Removing the trans. pan may also require you to remove or loosen crossmembers to allow removal of the pan. You want to remove the pan carefully because the filter screen assembly should be replaced if you are changing the fluid. It is easily seen when the pan is off and is removed by 2 bolts. Install new filter, put new gasket on pan flange and refill transmission with proper fluid and amount. See your owners manual for fluid type. On auto transmissions, engine must be hot, car on level and idling while checking proper level of fluid.
you change the manual transmission fluid in a '99 cavalier simply by removing the transmission drain plug and allowing all the fluid to drain then replace the plug and refill with Syncromesh transmission fluid(that is the fluid recommended by Chevy for use in your transmission) It should take 2 quarts.