How do you replace idler pulley on Ford Freestar?

To replace the idler pulley on a Ford Freestar, first, disconnect the negative battery terminal to ensure safety. Next, relieve tension on the serpentine belt using a wrench on the tensioner pulley, and remove the belt from the idler pulley. Unbolt the old idler pulley from its bracket, replace it with the new pulley, and then reattach the serpentine belt, ensuring it's properly aligned. Finally, reconnect the battery and start the engine to check for proper operation.