Human can do nothing to the aliens. This aliens. are intelligence and have a tech., Tech to move through space and time. And i think they have a real big guns. So nothing... you can do really nothing to them...
Human weapon is works only in Earth atmosphere. Like bullets, rockets...maximum it can be atomic rockets weapons. And i think this is maximum humans can show to aliens.
And i think this aliens have a mass destruction weapon. Some deadly lasers, or planet destroyers. Or just destroy atmosphere, change climate, add some ingridients to earth surface. So in this case humans has no chance.
But i think space is so huge, so aliens are really far away. And nothing to fear.