I train many women who are scared to perform strength training exercises for their chest or pectoral muscles for various reasons. Not only should you not be scared, but it is necessary for maximum muscle performance.  Performing chest exercises alone, will not make your breasts smaller. To say that would imply that you can spot reduce fat and you can not. Yes, as you lose weight if your body loses it in its breast they will get smaller. One way to slightly lift breast and build your pectoral muscles is by performing chest exercises

How many reps should I perform
12-20 reps, 3-4 sets=endurance, lean, toned
6-12 reps, 3-4 sets=building mass
1-5 reps, 3-4sets =maximal strength

My favorite chest exercises:

Dumbbell or cable chest flies
Dumbbell or barbell incline bench
Bench press

Strong chest Benefits for women:
1. Improves posture- a strong chest along with equally strong shoulders and back muscles, gives you better posture.
2. Prevents muscle imbalances-prevents stronger muscles from dominating over weaker ones which makes you more prone to injury and pain.
3. Makes performing other exercises so much easier: yoga movements, push-ups etc.

Start  incorporating strength training exercises for your chest into your weekly routine. Your pectoral muscles are just as important as your shoulders and back.