Tooth color can't be changed just like skin color. If your teeth are yellow, they will be yellow only. Trying to make them white may lead to more pale teeth.
Brush gently twice daily, use mouthwash, get teeth cleaning done to remove stains, calculus and plaque.
If yellow teeth is a very big concern for you then you can do laminates and veneers. But this involves slight tooth invasion. And veneers have a limited life.
Next Steps
Visit dentist for ultrasonic scaling.
Health Tips
Do not try any home remedies. They make teeth pale and sensitive.