To flush, or not to flush? (Transmission)

My ‘07 explorer was handed down to my teenager and we’re getting all the basic maintenance done. The last fluid on the list is trans. It has 145,xxx miles on it and I doubt it was ever done since I bought it with 28k miles.

I’ve heard a dozen stories of people who flush the Tran’s and then it goes out. Should I just top it off? It runs super smooth and has never overheated.