Here are the steps on how to change the transmission filter in a Toyota Sienna:
1. Raise the vehicle and remove the skid plate.
2. Locate the transmission pan and remove the bolts that hold it in place.
3. Carefully lower the transmission pan and drain the fluid into a drain pan.
4. Remove the gasket from the transmission pan and inspect it for damage.
5. Pry the transmission filter out of the pan.
6. Inspect the transmission filter for damage and replace it if necessary.
7. Install a new gasket on the transmission pan and reinstall the pan.
8. Reinstall the skid plate and lower the vehicle.
9. Add new transmission fluid to the vehicle.
It is recommended that you change the transmission filter every 30,000 miles or 2 years, whichever comes first.