2002 ford windstar tranny fluid?

How many quarts needs to be replaced if I do a transmission fluid change the van takes a total of 13.7 quarts I know if doing a flush would need to replace all of it but if just fluid change from pan and changing filter?

Drain the fluid to a no-leak container. Measure the fluid. Put the same quantity back.

What he said, or ask at the parts store when you buy the gasket and filter kit.