In the gym, you should have two options when it comes to modifying your girls' bodies. One is a "-" near each stats, allowing you to take off weight in unwanted areas, the other is a "+" and it works on all stats at the same time. You need to use the later one.
Also, you need to know that several times a day, the stats will change... adding or taking off some weight here and there. The only way to prevent this is to hire a trainer. And trust me, at 15CC for 2 months, it's definately worth it.
Otherwise, you'll have to work on their bodies on a daily basis.
**Edit** I made the correction regarding the time for the trainer.