Hello mam.
The food/ Beverages we consume, over time stain our teeth. Regular brushing will not be enough to remove those stains. In order for your teeth to be become white, there are Teeth Whitening kits available which a professional dentist can recommend.
They can be in office and at home treatments, usually can lighten upto 3 shades depending on the current. but these are not permanent results. Second option is Dental Veneers.
Next Steps
Visit a dentist for a consultation. Depending on your needs, the dentist would suggest whether to go for whitening or dental veneers.
Health Tips
Please don't follow any DIY tutorials on naturally whitening teeth. They do more harm than good