One should recite the following repentance in front of Buddha. If one recites sincerely, it will help to lighten our sins in the past and pesent life :
Followings is the nice version of Kuan Yin Pusa 普门� ( the complete scripture) :
http://www.youtube.com/watch?v=EETiZoSQn5s
http://www.youtube.com/watch?v=Wa-KXF9Fh10
http://www.youtube.com/watch?v=KVVequIzGvg
http://www.youtube.com/watch?v=T5LJgU2zB6o