I've had yellow teeth since I was child. It's very horrible when I smile. I want to change this. What can I do?

You have not provided photos, but basically you have two options.1.  Bleaching2. Porcelain VeneersSeek out a cosmetic dentist for a consultation and they will help you make an educated decision on what you should do.  

Professional teeth whitening services offered by your dentist will provide dramatically different results than over the counter whitening toothpaste. A dentist may also recommend alternatives, such as porcelain veneers. 

The easiest answer I can give you without photos is to try bleaching your teeth. This is simple and noninvasive. If bleaching doesn't work you might consider veneers. Talk to your dentist about your options.

There are many products out today that can whiten your teeth. The safest and smartest way would be to see your dentist and discuss what the best options are for you. The strongest whitening products are only available from a dentist. 

I would see a dentist to evaluate them first and if appropriate have your teeth professionally whitened. This may involve in-office as well as home whitening procedures to get your teeth to the color you want. If there are other issues going on, then veneers may be the solution, but whitening would be the least invasive and least expensive way to go first.