I'm trying to decide in what order I should do my workouts. I have a workout DVD for about one hour that consists of upper, lower and core body workouts. Then I do more working out for about 20 min. Every day I will runn up and down the stairs for 30 minutes. Im wondering if i should do the 20 min workout and run up and down the stairs on a seperate day that i do the workout DVD or do 20 min workout and DVD and not run up and down stairs that day. Which order and when should I do these excercises/workouts and why?

I'm a 16 year old female, 5'7 and a half 132 pounds

I'm also afraid that if I do the upper body workouts that I will lose my breasts and i do not want that. i wear a 36B