Where is the solenoid that controls gear shifts in an automatic transmission located at?

I'm trying to replace the selenoid that controls gear shifts for a 2001 ford taurus but need to know where its located at

The solenoids are inside the transmission. However if you are experiencing transmission problems, I hate to say it but the transmission itself might be toast. They are notorious for failure due to poorly designed internal lubrication channels. I could be wrong though. Anything is possible.