Upgrading the brakes on a Giant Anyroad 2 2015
You can directly change for BB7 without needing new rotors. 

If you want 160mm rotors with BB7, you would need new caliper mount adapters. Changing to 160mm rotors will give you slightly more stoping power, but whether it's worth it, is completely subjective. 

It's pretty straight forward to do. Once you get the bike, you can ask a specific question about it.