how do you identify and remove the males?

Look for pod sites which are the areas with emerging pollen pods, im not sure on the technical term.

 

Check this link.
It was the question asked 5 minutes before yours.
http://forum.grasscity.com/showthread.php?t=87332

 

If your are lucky your plants will preflower. Mine did about a week before I put them in flowering my last grow.(3 females, 1 male) and that was my first grow but I have read up a lot of shit. If they are females they will have little white hairs called pistils. and the males will have nothing or maybe little pollen sacs. sometimes this happens before flowering mostly I guess it happens the 1st or 2nd week of flowering. If you want to see pics they have some on hempcultivatioin.com in some of their forums.
goodluck!