Adding People to groups

Ok, I've gone blank on what I need to do to add some people to a group shot. I used the lasso and got the part of the first person I want to use, free transformed it to the size I need, but i can't seem to add him to the back row. I know I'm forgetting something simple, but I'm just blank. Please help.

Alan

Cut out the other people in the group and put them on a layer in front of the people you are adding.