Firstly you need to undergo cleaning ( scaling procedure) to remove tartar deposits.
If you need additional whitening of teeth you may go for tooth bleaching.
For more information visit
Whatever food and beverages we consume causes yellowing of teeth due to deposition of a yellow layer on teeth known as plaque and calculus. Scaling and oral prophylaxis will help in removing this yellow plaque and calculus from teeth. Visit your dentist for scaling. Also if you want to lighten your teeth shade further, you can ask for bleaching.
Brushing twice a day with soft brush in upside down fashion and regular use of mouthwash & floss will help in less deposition of plaque.