1995 Oldsmobile Aurora transmission gear shift

Transmission problem
1995 Oldsmobile Aurora V8 Wheel Drive Type unknown Automatic 143000 miles

I notice the transmission on the car is switching gears hard if at all while in Drive. I've checked the fluid level once there was no reading on the dipstick. Then checked it again about 15 min. Later and it was full. I was told the trans filter could be the cause and needs to be changed. Could you please give me your thought on what it could be and where the trans filter is located? Thanks!