Transmission sensor replacement

Greetings everyone. I need some advice on a transmission issue. One day a while back my check engine light came on and the transmission started acting funny. Took it to AutoZone and they checked it out for me. The read out said it was the transmission sensor. We looked up the part which ran about $86. No big deal there. I wanted to know how easy it is to replace this part myself. If it's gonna be a task and a half that will take a whole weekend I may check out to see how much it would run to have someone do it for me. I'd rather save the cash if I can, though working in this splendid heat is a tad of a deterrent. If anyone has any suggestions or can tell me where and how to replace this sucker I'd really appreciate it. Thanks!

Which sensor? There are 3. An input, output, and a speed sensor.