To access them, you would need to remove the transmission from the vehicle. This is a significant job requiring specialized tools and transmission knowledge. It's not a DIY task for the average car owner.
If you're experiencing transmission problems, it's best to take your Windstar to a qualified transmission specialist or mechanic. They have the tools, expertise, and diagnostic equipment to properly diagnose the problem and determine if a solenoid (or other internal component) needs replacing. Trying to locate and replace these solenoids without the proper knowledge risks further damaging the transmission.