People say that God created angels too right? so we know we're not alone right there. Are angels actual beings that "come down from the heavens" to visit us? Maybe all the stories of angels are actually aliens or maybe all the stories of aliens are actually "angels".
the world may never know!
Ir eally dont think most religions would change at all if aliens landed on earth. Most would find a way to work it into their beliefs and some religions already seem to have the possibility worked out ahead of time.