Hello! This solenoid is easy to get to with the pan off. And there are two solenoids that are identicle, the 1-2 and the 2-3 shift solenoids. It is usually advisable to do them both (as they are inexpensive and right next to each other.
With the pan removed., towards the back of the transmisison, you will see two square solenoids. Be careful removing these, as the 1-2 solenoid will be spring loaded. All you have to do is remove the retaining clip and pop the solenoid out of its bore.