17 years old, 5 ft. and 550 lbs. Based on the provided information, your Body Mass Index (BMI) would be approximately 107.66. This falls within the obese category.

Here's what to do to lose weight in a healthy way:

1. Eat a balanced diet with fruits, vegetables, lean proteins, and whole grains.
2. Control portion sizes and practice mindful eating.
3. Engage in regular exercise, including cardiovascular and strength training.
4. Stay hydrated with water and limit sugary drinks.
5. Choose nutritious snacks and limit unhealthy options.
6. Get enough quality sleep and manage stress effectively.
7. Seek support from healthcare professionals if needed.