Another transmission thread 90 lumina

I don't know anything about auto transmissions on these cars or most cars for that matter. This is probably a general question that isn't specific to my car but I have the 3.1 sedan and I think my transmission could use some maintenance.

When flooring the pedal the car will not shift and instead sits at redline. Just driving it around normal it's a fairly smooth ride with the occasional hard shift under heavier acceleration. I honestly don't know the last time if ever that this car has had the transmission fluid/filter changed (140k miles on it). I've been warned by some people against doing this as it could cause failure. Don't know if that's just an old wives tail or what but is there anything I can do to help the tranny out before it goes or keep it from going? Or would it be best to have it checked by a professional?

Correct, have it check by a pro, no one here can tell what's what without a road test.