How do i drain the tranny oil in an automatic 1991 firefly and change the tranny filter

Well the drain plug should be on the bottom of the transmission. It looks like an oil drain plug. MAKE SURE you DO NOT get these mixed up. Which means that one is used for draining the engine oil and the other on is for draining the transmission fluid. You just locate that plug and unscrew it and drain the transmission. That simple. Now to change the transmission fluid filter. You have to remove the transmission pan from the vehicle and replace the filter that is under the tranny pan and also replace the cork gasket that seals the tranny pan to the tranny. Then just bolt the pan back on and fill the tranny to the the fill mark on the dip stick. ( The dip stick is the stick that is used for checking the tranny fluid.) Hope this is helpful to you and good luck.

your best bet is to have some one show what to do or buy a repair manual from auto zone or any parts store. also to prevent over filling add 4 qts start the car let it warm up then check the fluid level and add as needed a pt.at a time. sometimes it helps to used a little silicone to hold the gasket in place. good luck.