To retain or build size in your hip three things you can do :

Strength training
squats, lunges, deadlifts and hip thrusts should be staples in your training regimen if your goal is to have “toned”.
curves.

Cardiovascular training

Not only will you build a stronger heart and build lung capacity, you will also burn fat and calories for weight loss. If done correctly you should see an overall reduction in body size and waistline.

Correct nutrition

Eating poorly will negate the benefits of strength training and cardio. A healthful diet is the main contributing factor to weight loss. A healthful diet entails caloric management and nutrition density.