removing character from background

Hi I wonder how to remove person, for instance from
and then replace him/her with other person dancing same song on green screen to look good. How to O.o also I quess lighting effects-good settings of it would be crucial ( mine has to be exact as in the raw video). I also got sometimes white dots on the screen – wonder what it is..

via Video Editing Forums: Digital Director – Adobe Premiere, Premiere Elements, and After Effects