Chevrolet: 2004 Malibu transmission

I have the small 4 cyl Malibu with autotransmission. I have about
170,000 miles on it. My wife reports occassional slipping as she
accelerates onto interstate. There apprears to be no way to check
trans fluid level. How can i drop the pan and change the filter (?)
and then replace missing or lost fluid.