Antenna direction and replacement questions

I have an Asus RT-AC68U. I'm experimenting with antenna direction and replacement. I hate to ask a dumb question, but what is the best placement for the three antennas? Angle the two outside antennas at about 45 degrees parallel to the router and let the middle antenna stand straight up? And to change positions, does the router need to be restarted?

I also have a paddle-like WL-ANT-157 that I borrowed from a friend. I assume it should replace the middle antenna? And is the "front" the side...

Antenna direction and replacement questions