hey,
The fit price and quality of KBC helmets are good - but the visor mechanism is pretty crappy. There should be a spring loaded latch that releases the visor. Open the visor all the way up, and look for the little latch (on the outside of the helmet) that you pull downward. Pull the latch down, and you can pop the visor out on one side then the other.
The problem with the latch is it's really small so it's hard to pull down (unlike Shoei's or HJC visor latches). But it's there.
The screws are to reposition the visor if it's leaking air when it's closed. With the visor off you can loosen the screws on each side with a thin flathead screwdriver and reposition it slightly. From my experience you can't get a really good seal on KBC's but they do the job.
Hope that helps,
Cheers